Remove dead code.
Move menu mux finding into mmux module.
Make config file parsing more generic.
Hook post-process steps into conversion process.

This includes:
 * layers
 * grouping containers
 * menu mux widgets
Tidy fix_layers.py.

Use utility function and log properly.
Add configuration files for new output structure.
Make smaller functions.
Ensure ordering of post process steps.
Merge branch 'post-process'