Distorted Android

Add DistortedGridFactory to share Grids among same-shaped DistortedObjects.

revert latest changes to the fragment shader.
small things in DistortedObjects.

remove the 'Color' vertex attribute.

Avoid a crash on exiting MessageSender

Minor: deal with IntelliJ warnings

minor

Important bugfix in the vertex shader: there was division by 0 in case Center point was on the edge of the Object, resulting in some vertices being shot into outer space.

Vertex3D almost finished - there's still a problem when parts of Cubes get culled if the Object gets Deformed or Distorted to the left (curiously only the 'left' direction seems to trigger this!)

Cleanup, consistent variable names, minor details.

Further progress with SenderThread: make it possible to actually exit the thread on app exit.