Jango service integration

First functional version of Jango service integration for Nuvola Player 3

Features of previous integration for Nuvola 2 are working: play / pause / thumb up / thumb down / song info and art.
At start-up, `track` object contains `title`, `artist`, `album` and `artLocation` with `undefined` value types (shown as string `<UNDEFINED>` in developer sidebar). You should find out where the `undefined` values come from and use ``null`` instead. (`Null` means no info available, `undefined` is considered as a programmer error.)