integrated and adjusted alembic for multi db configuration

added two migration scripts which could either be called
manually with
    alembic upgrade head
or for offline mode
    alembic upgrade head --sql
the migration as well is triggered in websetup.py from the
    python setup-app linotp.ini
if the config entries in linotp.ini are set to True

Change-Id: Ie563edc6bec1261f038593783a4b15f001df2f86