OpenGL ES Renderer: Finalize the last remaining bug fixes so that the…

… ES renderer can work "out of the box".

- Respect the draw buffers ordering rules that are unique to ES.
- Report the actual OpenGL variant being requested when initializing the renderer.
- Add oglrender_deinit() function pointer so that clients can properly handle the destruction of their associated context resources at the correct time.
- Certain internal OpenGL info is now assigned at run time instead of at compile time. This change now allows any of the OpenGL renderers to run side-by-side.