Reimplement monitor capture

- Implement windows monitor capture (code is so much cleaner than in
   OBS1).  Will implement duplication capture later

 - Add GDI texture support to d3d11 graphics library

 - Fix precision issue with sleep timing, you have to call
   timeBeginPeriod otherwise windows sleep will be totally erratic.

libobs-opengl/gl-windows.c

@@ -513,3 +513,8 @@ extern void gl_getclientsize(struct gs_swap_chain *swap,
 	*width  = rc.right;
 	*height = rc.bottom;
 }
+
+EXPORT bool gdi_texture_available(void)
+{
+	return false;
+}