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.
I'm wondering if I should just change the names of status fields, rather than creating this hash.  I find the user-visible names clearer.