state until image textures are ready to be used. New async.wait function
to help with this.

running. GLModel has to implement GLObject.ready() method.

via a new function async.idle (which abstracts away wx-iness). This
means that the status-bar is actually updated during startup.

uses this to prepare texture data, and GLObjects query ImageTextures to
make sure that they are ready - they are not drawn until textures are
ready. I have discovered that all my changes to prefilter were useless -
rgbvector/tensor vector texture is currently broken.