Bug 1030972 - Import tasks from Bugzilla

@bobsilverberg @Osmose r?
This fine needs to be regenerated as another migration has been pushed to `master` (although not yet deployed to prod). The name of this file will need to be bumped and the frozen data model needs to be updated. Also note that we're hitting a bug in South which is causing unnecessary migrations to be created for tables involving the User object, so those should be removed.