PostgreSQL migration: Reimplemented DBAL, authentication layer and user management modules in Hawat.

Base on the previous work the DBAL in Hawat was reimplemented to use the new mentat.services.sqlstorage module and sqlalchemy backend. The authentication layer was rewritten to use the new dabase interface. The user management plugin was rewritten to use new database interface.

(Redmine issue: #3752,#3734)