Update/rewrite of ofxONI1_5

Summary:
 - Removed threading, as it should not be necessary when using 1 kinect. OpenNI is already running in parallell, and updates can be done by IsUpdatedDataAvaiable and WaitAndUpdateData on the generators. 
 - Added UserData structure which stores all relevant data from the user tracker, i.e. status and skeleton points. Uses openFrameworks data types. Also added coordinate transform functions for openFrameworks data types.
 - Some refactoring and cleanup.