Added my_music, browse, discover and radio

Implemented:
* my_music
* browse (using tunigo API)
* discover
* radio

"Browse" can be improved a lot. Right now it always get a fixed number of items (this should be a param from outside) and it does a json parsing without much error checking. Anyway, it works.

I have tested this changes in a spotify plex plugin I am working at. I did my best to extract them, as there were plenty of related changes, let me know if you find something missing.

Hope it helps!