Distorted Android

1) Cube: convert it to the latest library. Main difference: objects are rendered better, individual cubits have rounded corners.
2) Examples: some adjustments to MeshJoin & Predeform
3) Library: fix a bug in main_vertex_shader's 'degree' function, which didn't work proprely in case of a vertex which was exactly at the center (i.e. vector PS was zero)

Progress with MeshJoin.

Progress with the Predeform app.

Progress with Predeform: UI for the list of Vertex effects to preapply.

Progress (?) with Predeform: give up trying to render the Mesh in Activity1.

Progress with Predeform.

Beginnings of a new 'Predeform' app which tests pre-applying a queue of Vertex Effects to a (single?) Mesh.
So far just a copy of Inflate app.

Change the Postprocessing effects: separate the radius and the halo.
Reason: we needed a way to specify the size of the halo around a postprocessed object; before it was automatically (and not very correctly) computed from the radius - before we knew the size of the object's bounding box, so this automatic computation was possible. Now we're removing the MashBase.getBounding(0 API, so the size of the halo has to be explicitly given by the user. This way is more correct anyway and gives the user more control (as the Multiblur app proves!)...

Move to AndroidX, target API level 29.

Minor.