Win8 touch support

This adds touch support for windows 8 pointers to direct input. Pointer 0 still has mouse fallback, so no feature loss on < win8. I had to pass window messages from the video driver to direct input - since this is win specific I didn't want to add to the input_driver_t struct and simply called the function directly. It might be possible to hook the window proc via driver.video_window if you don't want this direct connection.

Marking retroarch as dpi-aware via the manifest is required for correct coordinates in high dpi modes and also properly hides the taskbar in windowed fullscreen mode.