Make datetime display in local time zone

- Specifying time zone and format when inserting time into data store.
- TimeCop freezes to current time instead of 0000-0-0-0-0-0.
- TimeCop's Time class doesn't have access to the in_time_zone method,
  but for test purposes it should suffice to leave them in whatever time
zone, with a matching format.
https://github.com/amaabca/lita/pull/21