Refactor the versions system to utilize a new DB field 'recent_version_id'; speed up Scalar (especially on large pulls) by offloading the acquisition of a content's most recent version to a new DB field, 'recent_version_id', which is kept up-to-date with the most recent value (on save, delete, etc). A few extra lines are present here and there to ensure that legacy DBs without the new field work properly.