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.
The logic for how to open a file should be with the encoder. Currently we have two ways it seems call `open` for the stupid `CopyEncoder` and call `stream` with a `filesrc` for `GSTEncoder` ick.