Boost Ministers, Organisations, and Topical Events

These things are more important than news stories, speeches, etc. within
the Inside Government data model. This boosting gives them a relatively
higher weight versus other things that match, because users should
always be able to find:

- The G8 itself, versus a news article about the G8
- David Cameron versus an article about David Cameron visiting a
  hospital
- The Ministry of Defense versus an publication about HR within the MOD
Add Topics to list of boosted formats

This addresses @tarastockford's feedback, and has been discussed with
Inside Gov product management.
Merge pull request #49 from alphagov/inside-government-format-boosts

Boost Ministers, Organisations, and Topical Events