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!
debinding advisable, if you do something else between: it's cleaner. Speed : nothing, you're not in loop. Do you see ?