6996 - Dockerfile for build

Handle API error(s) in Tomtom matrix. Fixes #6884

- Update the form
- Use policies and update the seeds accordingly
- Add a link in the navbar(s)

I previously tried to correct a circular dependency problem in
a057276129b1f62b811743db3b8f867a05241ed3, but that didn't fix it (it was
intermittent, and came back).

After some wrangling, I've now deduced with some confidence that the
problem comes from `RouteWayCostCalculator`, which used
`TomTom::Matrix::RemoteError`. From the way it looks, this seems to mess
up the Rails autoloader since `tom_tom.rb` will try to load the `Matrix`
class from the `TomTom.matrix` call above. Or something.

In an attempt to fix the circular dependency error for real this time,
move the error class to a completely separate module from `Matrix`, and
refer to this when we need to use the error class.

Refs #6884

We might not always get a nicely formatted JSON
`['error']['description']` response body. Sometimes, like for example
when you use an incorrect API key, even with an 'application/json'
content type, TomTom will respond with:

    <h1>Developer Inactive</h1>

What?

In that case, the response has a 403 status. In addition to checking for
an error in the response, should also be checking for the HTTP status
code.

Log the status code in the exception to give us more information about
what went wrong.

Update our existing tests now that `#check_for_error_response` takes a
response object instead of a JSON string.

Refs #6884