Use escape_sql_id() for privileges SQL queries.

* glom/base_db.cc:
* glom/libglom/db_utils.cc:
* glom/libglom/privs.cc:
* glom/mode_design/users/dialog_groups_list.cc:
* glom/mode_design/users/dialog_users_list.cc: Use
DbUtils::escape_sql_id() instead of manually adding quotes with
no escaping. This seems to be the right thing to do for these
queries.