Added add/remove signals to scenes

Scenes will now signal via their source when an item has been added
or removed from them.

  "add" - Item added to the scene.
  Parameters:  "scene": Scene that the item was added to.
               "item":  Item that was added.

  "remove" - Item removed from the scene.
  Parameters:  "scene": Scene that the item was removed from.
               "item":  Item that was removed.

libobs/obs-video.c

@@ -56,7 +56,6 @@ static inline void render_begin(struct obs_display *display)
 
 	gs_ortho(0.0f, (float)width, 0.0f, (float)height, -100.0f, 100.0f);
 	gs_setviewport(0, 0, width, height);
-
 }
 
 static inline void render_end(struct obs_display *display)