Removed the DisplayGroupInterface and its subclasses.

Change-Id: I321b1064222ebc343e23276e1b6a5ef3f7ff236f
Removed obsolete support for Python, Skeletons and Joystick (OpenNI, SDL).

Change-Id: I8cb705d48d6542040347cf1826723b66070cdd3b
Finished removing DisplayGroupInterface

Change-Id: Ic0e71bb26637d02ad317a4e95e4b888cdf07cb23
Removing obsolete TouchListener (superseeded by MultiTouchListener).

Change-Id: I0ff03a363e691fe138b381681d776b002c324846
Merge pull request #111 from rdumusc/displaygroupinterface

Merged DisplayGroup and DisplyGroupInterface.