SqueezePlayer: Browse library and apps

[elParaguayo]

Plan is to add functionality to control basic manipulation of playlists (e.g. browsing library and adding tracks to playlist).

Should also add ability to use apps (e.g. Spotify).

This will not be easy!

Plan is:

• [x] Create module to access server using JSON RPC interface rather than telnet connection
• [x] Create module for accessing data required to generate menus
• [x] Update screen with menu functions
• [ ] Customise home menu
• [ ] Retrieve x items and then retrieve more when scrolled to bottom
• [ ] Tidy up code
• [ ] Replace telnet modules with JSON modules in main screen