[retroplayer] Added RetroPlayer, a new player core that enables game clients to play video and audio.

Thanks to elpendor for RGB565 support, poisson for RAII improvements and ChrisMyhre for catching a compile error.
[retroplayer] Added keyboard and joystick input handling to RetroPlayer built on the new joystick abstraction layer.
[games] Add new type of add-on, xbmc.addon.game, plugins and scripts that can be run from MyGames window
[games] Add MyGames window to the GUI
[game clients] Add win32 and linux repositories for game client add-ons
[joystick] - fix compilation if HAS_JOYSTICK is undefined
[osx/ios/atv2] - sync xcode projects
[cosmetic] Add TODO and, move TODO to header, and remove unneccessary debug statement
Fix game clients failing to find system directories when path has a trailing slash.

A string is a valid directory with or without a trailing slash. This means we can return either: prefer without, as the occasional game client author tends to concatenate without checking for the trailing slash.
Fix compile on windows
revert "X11: add SDL joystick until we have a better solution", functionality should be handled by "Joystick API (PR:2370 - https://github.com/xbmc/xbmc/pull/2370)"