graphics optimization feature inspirated by diablo3 engine

* the rendering now consits of two panes
- the background pane (for animated stuff like the map)
- the foreground pane (for steady stuff, like UI)
each pane has it own max FPS and works idependently
this may increase graphics performance on many platforms

modules/core_styles/styles/labels.otui

@@ -20,7 +20,3 @@ FlatLabel < UILabel
 GameLabel < UILabel
   font: verdana-11px-antialised
   color: #bbbbbb
-
-FrameCounter < UIFrameCounter
-  size: 68 16
-  align: right