Moved to Alembic

> Periodic schema updates were required, the old method of instantiating the DB was clunky for this as it tossed data.
> Now we use alembic and autogenerated migrations.

Other changes:
> Added indices on some match fields to speed up feature extraction.
> Fixed some default returns and /0 issues in features.py.
> Moved to parsing requirements.txt file to DRY deps.
> Updated README.md for new quickstart procedure.