Database upgrade

With this PR we can save all details for records that are available through the API in the database, including relations between records. An other big change is the way the anime-/mangalist is saved: this is now done by relation tables too, meaning that we can now save lists of other users (e.g. friends).

**Notice:** this PR only contains the backend-stuff for this, there are no visible changes, I left that part for @ratan12 ;)