Added rotate and scale shaders as copies of the translate one.
Changed background colour and window title.
checkGLError only has an implementation if -DDEBUG is provided.
Passing all of the vertex & element buffer to the GPU now.
Added camera to shaders and better validation to Cube draw method.
Enable OpenGL depth testing
Removed camera (no need to introduce this complexity at this stage)
Corrected projection matrix in shaders.