Get floor feature for ofxNITE

Added the getfloor() and getfloorconfidence() feature to ofxNITE
Get floor confidence does not seem to work (probably a nite problem)

The tricky part was that you can not call the readframe function twice otherwise it becomes a blocking function (see nite doc) so I had to put the User trackerframeref as a member of the object so I could use it to request the floor.