Fix all deprecation warnings

Change-Id: I546bfddd216d4faff751b58c90ea97ed3dc580d4
progress_bar is unused

Change-Id: I0d266006b7331c610035ab305b711d0aba2daf47
Use some rails_best_practices

Change-Id: Ia52467d76d853c54c0eecb4fb05ddd2e0076b32d
Remove unused methods

These have all been obsolete since the Great Gregor Refactor (~1 year
ago)

Change-Id: I11e20e0e0ae387551033979067d2841ee6b2d02d
Remove answer#{next,prev}

Change-Id: Ic9beab4f829ac7de0329fc464fe429aa5dfa7ba2
Reduce queries on overall leaderboard page

Change-Id: If54802bf7eb609e0daebd95db9fd396ca04ddc44
Avoid some broken admin routes

Change-Id: I375e2fe0826c25dc2803b16fcc233b28afff8edf
Simplify score calculation

Change-Id: I12b36de761196413a3fc24700763b0a7ac445448