This VREnvironment is independent from the JMonkey stuff and enables to
check and initialize VR specific capabilities before initializing
VRAppState.
The procedure is now to initialize a VR environment and, if the
initialization is ok, to attach a VRAppstate to the main application.
Some class has been refactored:
- System classes are within the com.jme3.system package
- VR related utility classes are in the package com.jme3.util.
