[BREAKING CHANGE] Changed the behaviour of the datepicker and datetimepicker classes for automatic datetimepicker initialisation:

1. All date pickers will have the class datepicker; all date+time pickers will have class datetimepicker
2. Date and time pickers by default have no start and end date/times. This can be overridden by using the data-startdate and data-enddate HTML 5 attributes
3. To ensure that only past or future dates are used, specify future-only or past-only; don't mix them!
Make all date time pickers include a hint on the expected date/time format for their inputs.
Properly implement the HTML5 data attribute specification for start and end dates for the datetimepicker. Remember to specify full ISO8601 dates.
Clean up the milestone time specification for creating events within a milestone period; this does not require gon and is generated server-side.