UI for choosing games

This pull request adds a UI allowing a user to select a game to stream (from among those available) after choosing a host to stream from. 

GFE provides a list of streamable games via its HTTP api, which I've presented in a new frame that comes up after selecting the Gamestream host. If a game is already running, this frame is not shown and the user jumps right into the running app. When a game is selected, the HTTP api is used to launch the game from GFE, and then the normal Limelight handshake+connection process is started.