Distorted Android

1st attempt to restore internal variables in Multiblur.

Still several problems, but the core of Multiblur works now.

Improve the Multiblur app. Things seem to work now!

Enrich the Multiblur app.

It now automatically chooses OpenGL ES 2.0 and GLSL 100 or OpenGL ES 3.0 and GLSL 300.

Postprocessing effects will not work on OpenGL ES 2.0 contexts.

as clearing Depth has been fixed in 580f7d10, we can now use this API in the 'FBO' app.

New 'glClearColor' and 'glClearDepthf' APIs in OutputSurface. This fixes the 'transparency' regressions from last commit.

Now there's a single place one can have a look at all the Meshes being rendered to a OutputSurface: OutputSurface.renderChildren().
This will need to get modified for per-object post-processing.

Minor

Speed up shaders (both compilation and execution) by explicitly enabling only the needed effects.