Sort topic groups by their parents.
Whitespace.
Short-form partial renders.
Reorder association inputs.

As per comments on https://www.pivotaltracker.com/story/show/76896710
Push fieldset legends closer to the fields they legend.
Add clearer warning about topics née specialist sectors.
Merge pull request #1703 from alphagov/restructure-specialist-tagging-interface

Restructure specialist tagging interface

https://www.pivotaltracker.com/story/show/76896710