Add option for stay on top "during video playback"

[scootergrisen]

MPC-HC has fourth option for stay on top, so it only stays on top while a video is player.

Sometimes i play music and when there are no picture i dont need to have the window on top, only when there is an videoimage.

So if you add an option like "during video playback" or whatever you want to call it then i dont have to change the setting each time i switch between music and video.