Disable overlay on host computer per-game

[neona]

Please give us the functionality to disable the overlay when streaming, at least for non-steam games. Previously this could be done via settings (though it affected all games), but now the overlay is forced on when streaming. Some non-steam games crash with the overlay enabled, and were previously streamable windowed with the overlay disabled.

Ideally, the best solution is probably to run the overlay client-side for latency reasons anyway. I'm aware that the overlay is used for controller input and fullscreen capture, but there's no reason it couldn't just have the key combo temporarily disabled on the host while streaming so as to not conflict.