sqlalchemy: update version requirements

* Updated minimum and maximum version requirements for SQLAlchemy and
  SQLAlchemy-Utils.

* Fix compatibility problems with invenio.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
sqlachemy: fix PostgreSQL drop tables

* Reimplement inveniomanage database drop utility to support PostgreSQL.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>