Playlist Support

I took a stab at adding some basic Playlist play support to the Roku client. This is the first time I've looked at the Roku client code and am sure I've made some mistakes.

Added a "Playlists" main menu item. 

Used the 'collection' thumbnail image for represent the playlist items.

![roku_playlist1](https://cloud.githubusercontent.com/assets/884816/4024016/17f8b110-2bb3-11e4-8350-dded3ab182b2.jpg)
![roku_playlist2](https://cloud.githubusercontent.com/assets/884816/4024018/1d585674-2bb3-11e4-98ab-1f23a2343fa9.jpg)

I've test with the QNAP (Intel) Plex Server version 0.9.9.14.5. Created the Playlists on the server side then accessed them via the Roku client.