fix small bugs
comment out new updates
comment out completely
Deleted old SQL files.

Two SQL schema files are not used anymore (they have been merged) - this commit
removes them.
fix transition matrix bugs
Changed name of column in usertags.

From `preferences` to `preference`.
Don't fail when e-mail cannot be sent.

Sometimes Postmark returns an error, e.g. when the recipient has been bounced
before. We just ignore these errors.
Improves raise messages when playlist creation failed.
Merge branch 'master' of https://github.com/lca4/unison-recsys
Updates solo_views api

Adds update_library() method to handle batch updates of user playlist library.
Existing update_playlist() is duplicated such that it can be called directly by
api or reused by update_library().