Add Win32 gestures helper

This is a helper to take action on touchscreens on Windows 7 or later
It uses the braindead WM_GESTURE API and supports volume, seek (1 and 2
fingers), play/pause (2finger touch) and fullscreen (zoom gesture)

The API is simple so other UI element can use it, notably Qt and the
vouts

This has been edited by jb too

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
Plug gestures on video output