Fix https://github.com/brainspec/enumerize/issues/224

The `#notify_parent` method should update the `notified_parent_at` field
on the child import so we know not to query it in subsequent batches of
parent import notifications.

Add the Timecop gem in order to be able to safely test the DateTime
update.

Refs #3511

Want a way to beautify HTML to get better diffs in the
`TableBuilderHelper` spec. Beautifying the HTML allows us to do line
comparisons of the HTML that results from the builder.

Refs #3479

This is a personal optimisation. If it doesn't make sense to add to the
project, we can remove it.

I want to be able to open the application's database console quickly at
times, and this gem lets me do that.

This gem allows RSpec to be used with the Spring preloader, eliminating
the Rails startup time when running tests. Was getting really annoyed at
the 10-second startup times every time I wanted to run any tests.

Here's a sample comparison running a single test file:

    Before:

    rspec spec/models/chouette/vehicle_journey_at_stops_day_offset_spec.rb
    Run options:
      include {:wip=>true}
      exclude {:js=>true, :meta=>true}

    All examples were filtered out; ignoring {:wip=>true}
    ...

    Finished in 2.01 seconds (files took 9.41 seconds to load)
    3 examples, 0 failures

    ---

    After:

    spring rspec spec/models/chouette/vehicle_journey_at_stops_day_offset_spec.rb
    Running via Spring preloader in process 45340
    Run options:
      include {:wip=>true}
      exclude {:js=>true, :meta=>true}

    All examples were filtered out; ignoring {:wip=>true}
    ...

    Finished in 2 seconds (files took 0.76843 seconds to load)
    3 examples, 0 failures

When doing TDD this is a huge workflow improvement.

Since the `/bin/` directory is ignored by .gitignore, you'll have to
generate the binstub manually to get this working:

    $ bundle exec spring binstub rspec
    $ git checkout bin/spring  # since this file is in the repo but is
    $                          # also in .gitignore so shouldn't be
    $                          # committed.
    $ bundle exec spring rspec  # enjoy!

To use with rspec.vim, add this to your Vim config:

    let g:rspec_command = "!bundle exec spring rspec {spec}"