REFACTOR: Replace score bonuses with low/med/high priorities

We removed score from the UX so it makes more sense to have sites set
priorities instead of score bonuses.

app/models/reviewable_user.rb

@@ -103,6 +103,7 @@ end
 #  created_by_id           :integer          not null
 #  reviewable_by_moderator :boolean          default(FALSE), not null
 #  reviewable_by_group_id  :integer
+#  claimed_by_id           :integer
 #  category_id             :integer
 #  topic_id                :integer
 #  score                   :float            default(0.0), not null