mod_authz_internal: Use util.roles, some API changes and config support This commit was too awkward to split (hg record didn't like it), so: - Switch to the new util.roles lib to provide a consistent representation of a role object. - Change API method from get_role_info() to get_role_by_name() (touches sessionmanager and usermanager) - Change get_roles() to get_user_roles(), take a username instead of a JID This is more consistent with all other usermanager API methods. - Support configuration of custom roles and permissions via the config file (to be documented).