Blender Git Loki

DRW: Shader Deferred compilation: Use a wmJob for threading.

Also get rid of the static var and initialization.
This enables the user to see the progress on the info header.
Closing blender or reading a file also kill the job which is good.

Unfortunatly, this job cannot be interrupt by users directly. We could make it interruptible but we need a way to resume the compilation.