"Poor man's" fix for changed passwords not being considered by Ampache API

Should fix https://github.com/owncloud/apps/issues/313.
This is however not an optimal solution: The drawback is that the user has to login at least once with the new password in the web interface. But that's a general problem of using the login listener I would say; even for first copying of the user to the media_users table it would be best to react on user creation directly, because at the moment, a user has to login at least once into the web interface before being able to use Ampache via the remote API.

So a better solution might be a hook to register listeners to changed user data (or specifically passwords?) - I'm open to suggestions ;)

If the changed password hook is the preferrable solution, then i would be glad about hints about the hook&listener design in owncloud!