Add a helper method for generating tracking links
Add an authority name to track descriptions if appropriate.

This is still brittle, badly phrased in some cases, and hard to
translate.
Merge branch 'feature/redesign-prep' of ssh://git.mysociety.org/data/git/public/alaveteli into feature/redesign-prep
Move track_set to the application controller.

We'll want to use it from the public body controller now, so make it a
widely accessible but private method.
Support the creation of a track from the public body page.
Merge branch 'feature/redesign-prep' of ssh://git.mysociety.org/data/git/public/alaveteli into feature/redesign-prep