GUI-overlay added!

new functional gui overlay

switching drawing funktion

files:
	modified:   ObjectManager.cpp
	modified:   ObjectManager.h
	modified:   UI.cpp
	modified:   angTest.cpp
	modified:   glut_backend.cpp
	new file:   gui.cpp
	new file:   gui.h
	modified:   lighting_technique.cpp
	modified:   lighting_technique.h