Squashed commit with OpenNI2Driver fixes and improvements

Fixes and Improvements for OpenNI2DeviceDriver:
- FIx CmakeLists.txt so IOpenNI2DeviceDriver.h is getting installed.
- Fixes for a bug that could appear with multiple users being tracked
- Improve and streamline the YARP port output of the device so it outputs only the currently tracked users, reducing the traffic and making it easier to parse