Better OpenGL performance and animation smoothness

[vbousquet]

This PR contains the change discussed in issue #283

There were 2 problems:

• SharpGL implementation performs rendering in a FBO, then copy the FBO to the native window. This copy was somewhat inefficient, and the code did trigger a GC at each copy leading to poor performance. This is discussed here dwmkerr/sharpgl@c436fef and here FBORenderContextProvider optimization dwmkerr/sharpgl#145.
• The other issue is that the implementation used a fixed rendering loop (timer based at a fixed framerate). The rendering frequency was not the one of the DMD source, leading to animation stuttering. This was not a performance problem but gave bad smoothness and lead to a perceptions of stutter and a feeling of a performance issue.

The PR change this by:

• implementing our own OpenGLControl based on the proposed fix in the previous links,
• modify rendering to be event based instead of render loop based, triggering a render each time a frame is submitted by the DMD source.

[vbousquet]

Sorry, I was to fast. I will take a bit more time to prepare a clean PR with its own branch. Closing for the time being