[retroplayer] Added RetroPlayer, a new player core that enables game clients to play video and audio.
Squash into "[game clients] Refactor game client serialization into its own class"
[retroplayer] Audio: Fixed delay on ALSA devices, and disabled audio delay setting in game settings.
[retroplayer] Added RGB565 support.
[retroplayer] Added keyboard and joystick input handling to RetroPlayer built on the new joystick abstraction layer.