Added Graphic support
I've added a few more unit tests for the Simple Integrator case. Also modified System.cpp and Body.h to create functions to help with calling unit tests
Changed declaration of RK4Integrator
Modified System to take pointer to parent class
Merge branch 'opengl' of github.com:martinmr/6.S096 into opengl
Fixed bugs in RK Integrator
cast sqrt(dampingFactor) to float)
Fixed RK4Integrator
Merge branch 'opengl'

Conflicts:
	include/nbody/System.h