Wip/texturing cube

Working well with CubeDirt and CubeSand. 

TODO: clean code

Do we have to unbind the vao and rebind it? 
file: testCubeGLInstancedRendering.cpp 
line: 131

I will check after LE FOIE GRAS!
because we have only one vao and we're in main loop, we don't need to bind unbind vao