Migrating submissions from old phase to new phase

Ready for functional review/QA/staging!

- [x] Use leaderboard entry as submission to move, if no leaderboard entry grab latest
- [x] `auto_migration` phase flag
- [x] `http://domain.com//competitions/check_phase_migrations` url, pinged every 3 hours
![image](https://cloud.githubusercontent.com/assets/2185159/3311441/a95bf956-f6c4-11e3-8cda-d314cac2aba4.png)

Made the button disabled and it gives a descriptive message