Fracas2 initial checkin - not playable

For now it only loads levels and shaders, creates a world with the
first level, inits the GL buffers with the world’s walls, and starts
the rendering loop. There’s no visible animation yet.
The code is like test 16, but object oriented. Initial maps are copied
from plexode.com/fracas. There’s centralized async task handling, since
the task tree is getting more complex.