[WIP] Native votes support: removed votes columns from migration script and schema, added conversion routine to convert old votes format (as text blob) to hive_votest table

[WIP] list_commments implmemenation: added native database_api.list_comments, raw_json data moved to proper table columns in hive_posts_cache, engine changed to support new columns. Added script to perform database upgrade.

[WIP] Works on sync and removing get_content call to download comment data. NOT TESTED! Probably will mess your db badly!