Distorted Android

Simplify setting up DistortedScreen.

Beginnings of support for DistortedEffects.drawPrivFeedback()

Progress with TransferFeedback app - introduce two modes: USEPOINTS 'true' or 'false'.

On Nexus5X, it works with 'true' and 'false'. On Nexus 4, it works with 'true', but returns GL_INVALID_OPERATION with 'false'.

Progress with Transform Feedback.

Progress with VBOs - this time abstract out a new class, DistortedObject - i.e. everything that uploads something to GPU and thus needs to be auto re-created upon loss of the context.

Revert "Major refactoring: convert the Matrix Effects to be independent of the resolution of the surface we render to."

This reverts commit d79a56d3bc6cc7a22b21abeb180353a1818bd6ad.

Major refactoring: convert the Matrix Effects to be independent of the resolution of the surface we render to.

Re-write the first 15 apps to work with this.

Major:

1) in the Library, fix the fact that some applications (those that were creating their DistortedSurface objects outside of onSurfaceCreated or onSurfaceChanged) would not render after the activity went to background (press POWER to see that).
2) in the Apps, call the new 'Distorted.onPause()' API to fix the above problem...

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.

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