* FIX: Store Reviewable's force_review as a boolean.
Using the `force_review` flag raises the score to hit the minimum visibility threshold. This strategy turned out to be ineffective on sites with a high number of flags, where these values could rapidly fluctuate.
This change adds a `force_review` column on the reviewables table and modifies the `Reviewable#list_for` method to show these items when passing the `status: :pending` option, even if the score is not high enough. ReviewableQueuedPosts and ReviewableUsers are always created using this option.
