Add UKVI topics as specialist sector tags

First part of https://www.pivotaltracker.com/story/show/65891232
Prevent indexing specialist publisher formats

We may choose to allow them to be indexed at a later date.
Merge pull request #131 from alphagov/prevent-indexing-specialist-publisher-formats

Prevent indexing specialist publisher formats
Merge pull request #130 from alphagov/add-ukvi-topics

Add UKVI topics as specialist sector tags

https://www.pivotaltracker.com/story/show/65891232