Use Google Music from inside Jukebox

What
---
Using gmusicapi Jukebox now supports the use of GoogleMusic accounts.

Adding a new GooglePlayStorage('username', 'password') 

What is still to do:
Add MultipleStorage to access multiple users accounts as well as local accounts.
Have a smarter Authentication layer when the session expires.
We should change the `Song.path` to `Song.url` and have the on disk files just start with file://