Further work on refactoring the camera API. Added proof-of-concept...
Further work on refactoring the camera API. Added proof-of-concept implementation into MprRenderer and MprDemo. Thereby fixed various issues of the new CameraData API that occured: * tgt::Navigation::updateClippingPlanes() yielding NaNs if the scene bounds were not defined * NumericProperty yielding endless loops in case of NaN values * Updated AbstractProcessor::process() to automatically validate level XYZ after calling updateXYZ(). * Adapted changes through renaming tgt into cgt refs #141 refs #386