Translation links generate based on current action

This commit removes a kind of complicated helper which generated a link
to a translated version of a resource.  Given there aren't any translation
links away from the given resource page, it would be easier to generate
the links based on the current controller action.

This fixes https://www.pivotaltracker.com/story/show/62057862
Move translation link test into pub controller test

This test wasn't working simply because there was no available route
for the tested controller action.

Why we are doing view tests in an abstract controller I've got no idea.
I can only assume it's because <%= random_legacy_reason %>.
Merge pull request #1253 from alphagov/fix-translation-links

https://www.pivotaltracker.com/story/show/62057862

Translation links generate based on current action