WIP on changing promotion to upvote/downvote.

This requires an unfortunate amount of additional methods for removing
upvotes and downvotes, as well as casting them. Promotion is determined
via a score rather than just the presence of a vote.

An odd bug as surfaced whereby adding another annotation to the fixtures
starts breaking the doc unit listing tests.
WIP on changing promotion to upvote/downvote.

This requires an unfortunate amount of additional methods for removing
upvotes and downvotes, as well as casting them. Promotion is determined
via a score rather than just the presence of a vote.

An odd bug as surfaced whereby adding another annotation to the fixtures
starts breaking the doc unit listing tests.
Merge branch 'voting' of github.com:mikesname/ehri-rest into voting
Rename methods back to promotion/demotion and uncomment test
Make promotion/demotion methods return the affected object
Add a cached score property to promotable items (and more tests)