Cleaned MPIChannel. Added: PixelStreamFrame, GLTexture2D, Renderable, TestPattern.

Change-Id: Ib01d80a4313140730f4b33d085c19d232eb829d1
Multiple cleanups following Ahmet's code review.

Change-Id: I4e309a6aa1c27755f1be55c9d484a85c704d00a9