db: add Alembic "migration environment" Add in kallithea/alembic an unmodified Alembic "migration environment", as generated by 'alembic init': Copyright (C) 2009-2016 by Michael Bayer. Alembic is a trademark of Michael Bayer. Also update LICENSE, MANIFEST and setup metadata.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.