More plan work
Added json type to sqlachemy, continuing work on plans.
Swapped json with ujson since it's faster.
1) Swapped out json for ujson in the json object
2) Switched trial_days to trial_interval to have much trial flexibility
3) Documented plan objects
4) trial_interval and plan_interval now use dictionaries to define the intervals

Next: Testing the plans.
1) Fixed DB engine
2) Wrote plan tests, all pass
3) Fixed plan query statements
4) Added uniqueconstraint of on plan_id AND marketplace
5) Datetimes now use UTC timezone
6) Created create_table script
7) Added billy error clasess: NotFoundError, BadIntervalError, and AlreadyExistsError