added admin actions to admin controllers songs and videos
added contents to model news, changed "thumb" field name to "cover" in _fields partial for admin news, added callbacks to admin news controller for artist not found
added missing parts of db schema
added common hooks for inserting to artists, updated artists, removed from artists, modified model Post, modified admin controller news
syntax tuned
moved common functions to common lib
modified releases fields for db schema
added contents to release model, modified admin controller releases for model