Voting Tidy Up and Note Refactor

This PR adds no additional functionality but instead tidies up things under the hood.

- Votes get deleted when a suggestion gets deleted (e.g. when a user leaves a chapter)
- Notes are now a first class entity.  This allows people to add notes to existing suggestions.
- Votes are now used in the pick page for "suggested by"
- Migrations squashed - this requires a database drop on production.