Restrict the length of the user agent

Because the user agent is persisted, the allowed length can't be longer than
the allowed length in the storage.
Merge pull request #133 from alphagov/add-user-agent-validation

Restrict the length of the user agent
Add rel='external' to external links

This renders a little icon next to external links.
Merge pull request #134 from alphagov/add-external-rel-to-external-links

Add rel='external' to external links
Change email input field type to 'email'

This ought to bring small usability improvements (eg email-specific keyboard on mobile safari)
Merge pull request #135 from alphagov/correct-input-type-on-contact-form

Change email input field type to 'email'
Remove the 'support-api' feature flag

The support-api is humming along nicely on production, so it's no longer
necessary to keep the feature flag for switching between the two apps.
Merge pull request #136 from alphagov/remove-support-api-feature-flag

Remove the 'support-api' feature flag
Fix specs to work with new `static` version

Recent change in `static` ([1](https://github.com/alphagov/static/pull/441),
 [2](https://github.com/alphagov/static/pull/445)) changed how
the `report-a-problem` mark-up and JS code work, which meant that some specs in
this app broke. This change fixes those specs.
Bump slimmer to v5.0.0

This picks up the automatic report-a-problem form, which means that the form
can be removed from this app (and the appropriate header set in places where
it's not desired).
Merge pull request #137 from alphagov/bump-slimmer-for-automatic-report-a-problem

Bump slimmer for automatic report-a-problem
Extract 'report-a-problem' hiding into ApplicationController
Merge pull request #138 from alphagov/refactor-report-a-problem-hiding

Extract 'report-a-problem' hiding into ApplicationController