mmdevice: adapt for Windows Store apps

The most important point is that we can not enumerate or active devices anymore
http://msdn.microsoft.com/en-us/library/windows/desktop/jj128298(v=vs.85).aspx
says we must activate the device from the main UI thread, which we can not access
from VLC C code.

Add a module option so the main UI code can activate the audio interface and pass
down that pointer to VLC.

ifdef out unneeded device handling code