Camera rework, crosshair and targetting

So this is some intermediate state, I'm open to see it rejected as it disables all old hud-features for the moment. 

It adds:
* Camera following player with inertia
* Camera chooses offset to player based on size of playership
* CrossHair can be used to target objects with the mouse
* Base architecture for stereo/mono support (independently moveable CameraHead with attachable CameraEyes; CameraDolly follows player)
* Adds HUD as sphere on which its elements will be placed and move around, see crosshair

If you think I should continue this until the HUD is fully useable again, feel free to leave critics nevertheless.