Initial Plex support

Based on work by joen-mauritzon but using the Json api.
Currently only library is supported more things to come.
Support for "Now Playing"

Currently only one item at a time.
Resize and convert all images to jpg before downloading them from the Plex server.
Update plex.py

Resize in Plex instead of in PIL. This will only cache rezised images.
Fix for loading images from Plex
Don't try to load images that doesn't exist.
Support for recently added

Need some work to coexist with XBMC.
WOL support, library update support, works together with XBMC and lots of bug fixes.
Hide viewed items and basic music support.
Support for playback control on clients that supports it.
Update plex.py
Added GDM, bug fixes and start items from library.
Fix Conflict
Some bugfixes
Some incorrect labels.
Fix for "limits" when a section doesn't contain any items
Fix for last commit that broke playback controls.
Fixed: toggle the play/pause icon
Fix load of movies from 50 to 100 in movies tab.
Always return playing_items and multiple players.