* Added exclusions module with a fully implemented ExclusionsDB that can pull
  from multiple sources for different sites.
* Moved CopyvioCheckResult to its own module, to be imported by __init__.
* Some other related changes.

Obviously this can and should be improved significantly later, but it seems
good enough for now.

Also implementing MWParserFromHell, plus some cleanup.

Conflicts:
	earwigbot/wiki/constants.py
	earwigbot/wiki/copyvios/__init__.py
	earwigbot/wiki/page.py