implement sql migration support for QonoS

- initialize a new migration repository, 'migrate_repo'
- add version scripts to create tables as declared in models.py
- introduce CLI, 'qonos-manage' to run migration commands like,
  version_control, db_version, db_sync, downgrade & upgrade
- make 'qonos-api' db initialization to add the database to the
  migration repository for version control
- implement tests for testing the migration & changeset scripts.
- add 'sqlalchemy-migrate' dependancy to the pip-requires
- introduce MANIFEST.in for including migration config files as part
of the distribution package.