Add timestamps to subreddit banlist JSON

Updates jsontemplates.py to include `created` and `created_utc` in subreddit user ban list JSON (e.g. /r/sub/about/banned/.json)

Clean up JSON Templates for RelTableItem and subclasses

fix typo in call to self.thing_attr

call direct parent class RelTableItemJsonTemplate instead of ancestor class ThingJsonTemplate

remove unrelated whitespace changes; don't redefine duplicate class methods

fix typo

remove additional duplicate class methods

clean up long UTC timestamp conversion line

remove duplicate class methods

remove duplicate class methods (again), remove duplicate class attribute declaration

misc cleanup

note should be empty string if not found