Role Translations in the UI should be configurable in local_settings.py

In adjutant-ui we have a hardcoded list of role translations. We should move this (and the util function that uses it) to the api module, and get source the role translations from the settings file, with the existing role translation values as the defaults for backwards compatibility.

https://github.com/openstack/adjutant-ui/blob/master/adjutant_ui/content/project_users/utils.py#L17-L33