Was getting these failures after switching the controller over to use a
decorated `@time_table`:

    Failures:

      1) /time_tables/show should render h2 with the time_table comment
         Failure/Error: - @time_table.action_links.each do |link|

         ActionView::Template::Error:
           undefined method `action_links' for #<Chouette::TimeTable:0x007fc8cefb8260>
         # ./app/views/time_tables/show.html.slim:13:in `block in _app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'
         # ./app/helpers/newapplication_helper.rb:246:in `block (2 levels) in pageheader'
         # ./app/helpers/newapplication_helper.rb:244:in `block in pageheader'
         # ./app/helpers/newapplication_helper.rb:243:in `pageheader'
         # ./app/views/time_tables/show.html.slim:4:in `_app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'
         # ./spec/views/time_tables/show.html.erb_spec.rb:15:in `block (2 levels) in <top (required)>'
         # -e:1:in `<main>'
         # ------------------
         # --- Caused by: ---
         # NoMethodError:
         #   undefined method `action_links' for #<Chouette::TimeTable:0x007fc8cefb8260>
         #   ./app/views/time_tables/show.html.slim:13:in `block in _app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'

      2) /time_tables/show should render a link to edit the time_table
         Failure/Error: - @time_table.action_links.each do |link|

         ActionView::Template::Error:
           undefined method `action_links' for #<Chouette::TimeTable:0x007fc8cb65b148>
         # ./app/views/time_tables/show.html.slim:13:in `block in _app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'
         # ./app/helpers/newapplication_helper.rb:246:in `block (2 levels) in pageheader'
         # ./app/helpers/newapplication_helper.rb:244:in `block in pageheader'
         # ./app/helpers/newapplication_helper.rb:243:in `pageheader'
         # ./app/views/time_tables/show.html.slim:4:in `_app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'
         # ./spec/views/time_tables/show.html.erb_spec.rb:20:in `block (2 levels) in <top (required)>'
         # -e:1:in `<main>'
         # ------------------
         # --- Caused by: ---
         # NoMethodError:
         #   undefined method `action_links' for #<Chouette::TimeTable:0x007fc8cb65b148>
         #   ./app/views/time_tables/show.html.slim:13:in `block in _app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'

      3) /time_tables/show should render a link to remove the time_table
         Failure/Error: - @time_table.action_links.each do |link|

         ActionView::Template::Error:
           undefined method `action_links' for #<Chouette::TimeTable:0x007fc8cd251820>
         # ./app/views/time_tables/show.html.slim:13:in `block in _app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'
         # ./app/helpers/newapplication_helper.rb:246:in `block (2 levels) in pageheader'
         # ./app/helpers/newapplication_helper.rb:244:in `block in pageheader'
         # ./app/helpers/newapplication_helper.rb:243:in `pageheader'
         # ./app/views/time_tables/show.html.slim:4:in `_app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'
         # ./spec/views/time_tables/show.html.erb_spec.rb:25:in `block (2 levels) in <top (required)>'
         # -e:1:in `<main>'
         # ------------------
         # --- Caused by: ---
         # NoMethodError:
         #   undefined method `action_links' for #<Chouette::TimeTable:0x007fc8cd251820>
         #   ./app/views/time_tables/show.html.slim:13:in `block in _app_views_time_tables_show_html_slim__2702796193816469913_70250218141540'

    Finished in 2.44 seconds (files took 0.82818 seconds to load)
    3 examples, 3 failures

    Failed examples:

    rspec ./spec/views/time_tables/show.html.erb_spec.rb:14 # /time_tables/show should render h2 with the time_table comment
    rspec ./spec/views/time_tables/show.html.erb_spec.rb:19 # /time_tables/show should render a link to edit the time_table
    rspec ./spec/views/time_tables/show.html.erb_spec.rb:24 # /time_tables/show should render a link to remove the time_table

To match the controller, we need to decorate the `time_table` objects
used in these tests as well, because the view code has changed.
Decoration is necessary to give us the `#action_links` method that we
use to render the header links on the page.

Refs #3479

The tests failed because we weren't using a decorated `Chouette::Line`
object, but the views now expect decorated lines in order to be able to
call the `#action_links` method.

Here are our failures:

    5) /lines/show should render h1 with the line name
       Failure/Error: - @line.action_links.each do |link|

       ActionView::Template::Error:
         undefined method `action_links' for #<Chouette::Line:0x007fc8cdf0bb88>
       # ./app/views/lines/show.html.slim:10:in `block in _app_views_lines_show_html_slim___3813514632397395671_70250211127360'
       # ./app/helpers/newapplication_helper.rb:246:in `block (2 levels) in pageheader'
       # ./app/helpers/newapplication_helper.rb:244:in `block in pageheader'
       # ./app/helpers/newapplication_helper.rb:243:in `pageheader'
       # ./app/views/lines/show.html.slim:2:in `_app_views_lines_show_html_slim___3813514632397395671_70250211127360'
       # ./spec/views/lines/show.html.erb_spec.rb:16:in `block (2 levels) in <top (required)>'
       # -e:1:in `<main>'
       # ------------------
       # --- Caused by: ---
       # NoMethodError:
       #   undefined method `action_links' for #<Chouette::Line:0x007fc8cdf0bb88>
       #   ./app/views/lines/show.html.slim:10:in `block in _app_views_lines_show_html_slim___3813514632397395671_70250211127360'

    6) /lines/show should render a link to remove the line
       Failure/Error: - @line.action_links.each do |link|

       ActionView::Template::Error:
         undefined method `action_links' for #<Chouette::Line:0x007fc8cfdaa710>
       # ./app/views/lines/show.html.slim:10:in `block in _app_views_lines_show_html_slim___3813514632397395671_70250211127360'
       # ./app/helpers/newapplication_helper.rb:246:in `block (2 levels) in pageheader'
       # ./app/helpers/newapplication_helper.rb:244:in `block in pageheader'
       # ./app/helpers/newapplication_helper.rb:243:in `pageheader'
       # ./app/views/lines/show.html.slim:2:in `_app_views_lines_show_html_slim___3813514632397395671_70250211127360'
       # ./spec/views/lines/show.html.erb_spec.rb:31:in `block (2 levels) in <top (required)>'
       # -e:1:in `<main>'
       # ------------------
       # --- Caused by: ---
       # NoMethodError:
       #   undefined method `action_links' for #<Chouette::Line:0x007fc8cfdaa710>
       #   ./app/views/lines/show.html.slim:10:in `block in _app_views_lines_show_html_slim___3813514632397395671_70250211127360'

Update the test to decorate the lines used in them.

Turn `current_organisation` into a `context` field on `LineDecorator`
because otherwise it's a global variable that comes from wherever that's
required in `LineDecorator`. And we'd have to mock
`current_organisation` on `line` in the test, which I wasn't keen on.

Refs #3479

Refs #3657