Adds support for the database relation, including:
 * Updating the settings so that during db-relation-changed the first
   database relation is used as the default django database.
 * documenting (via the Makefile) the custom steps required to ensure
   that the debversion postgresql type is available on the postgres
   service.
 * Adding a syncdb 'hook' (really a task), which can be called via juju
   run.
 * Removing south from the installed apps due to the broken migration,
   instead creating the tables in teh currently defined state (although
   south is still required on the python path due to being imported by
   the app).