STYLE: Document SlicerWizard/CMakeParser.py

Add documentation of SlicerWizard.CMakeParser. Tweak an exception
message that I noticed in the process could be improved.
STYLE: Make ExtensionProject.project a property

Change the project() method of ExtensionProject to a property, and
update uses accordingly.
STYLE: fix indent

Fix indentation of __all__ values in GithubHelper.py and Utilities.py,
which were using four spaces instead of two due to being copied from
another location that uses four-space indent.
BUG: Fix CMakeParser.py parsing

Add some additional escapes which were not being handled. Remove
attempts to parse expansions; AFAICT they don't impact argument
splitting (which is what we really care about), and the existing logic
was inadequate.