Oculus Rift support; Crosshair; Quite some architecture stuff

...aaand another big one. Let me try to summarise:

* Adds Oculus Rift support, that includes stereo rendering, headtracking and distortion-postprocessing (#259)
* Adds a CrossHair for scenegraph based, accurate shooting on objects (#258)

#### Complete rework of the rendering process
* Adds Scene and GameScene to assemble everything to be rendered. More possible Scenes would be MainMenuScene etc...
* Adds a Viewer, that renders a Scene from the perspective of a CameraHead using a MonoView or a StereoView
* Adds the CameraDolly that follows a worldobject using a CameraFollowHelper to keep appropriate distance (#257)
* Adds the CameraHead, that is mounted on a CameraDolly but can be orientated independently (#257)

#### Minor stuff
* Extract Object-Initialization from Game to GameScenario
* Make Player owner of his HUD
* Rework HUD as to place its elements (currently only one) on a curved plane rather than an even plane (looks better, integrates good with rift)
* Add limited WindowManager (no fullscreen/windowed toggle, no handy monitor-handling) 
* Add basic CommandLineParser

Downsides:
* Apart from the CrossHair, there is no HUD anymore/yet. Work on this will begin next week.
* On Linux the game crashes sometimes when entering fullscreen-mode on startup

To test stereo rendering, start the program with -stereo. To use an attached Rift, start with -hmd