Add Mozilla's preprocessor.py and makeutil.py

Source: https://mxr.mozilla.org/mozilla-central/source/python/mozbuild/mozbuild/preprocessor.py
Docs: https://mxr.mozilla.org/mozilla-central/source/build/docs/preprocessor.rst
Change Makefile: add .build dir, usage preprocessor.py
Move some css code to skin/shared/oops-box.css.inc
Rename .css.inc to .inc.css