common: Add window-x/y/width/height properties to blitter video sink

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>
common: Change blitter region rectange to use x1,y1,x2,y2

This is more suitable for a wide variety of operations, as opposed to
x,y,width,height

Signed-off-by: Carlos Rafael Giani <dv@pseudoterminal.org>