Improvements to hint administration

- Renamed level_source_hints/ to review_hints.
- Added pagination when reviewing hints.
- Added filtering by status.
- Added new status value for new hints (currently null until set by a reviewer).
- Dropped useless columns from display.
- Used source field so only crowdsourced hints are accessible through the GUI.
why are you defining constants and maps of those constants to user-visible names instead of using ruby symbols?