WindowManager.cpp

* Using single font instances per text group (adds flexibility, avoid font change during render)
* initialize() and resize() are now virtual, and overridden in subclass
* HUD dimensions now follow actual size (no more scaling needed)
* No more FSAA needed
* Removed unnecessary Open GL calls during render

Pro:
- Crystal clear HUD text
- Constant HUD text size
Con:
- Slightly higher CPU usage (5% -> 7.5%, also for full screen?)