Added GraphQL Support + Bugfix

[mathg]

Context

There was a bug in the rrule function that needed to be fixed and also added GraphQL support to at least return next and all occurrences through the api.

Added

• Calendarize Type for Graphql. It returns the next occurence in the form of an array of timestamps [start, end]. It also returns an array of all occurrences in the form of an array of array of [start, end].

Fixed

• In the CalendarizeModel rrule() function there was an error in the config where when there were no repeats, the UNTIL was using startDate instead of endDate
• In the javascript file, when adding a TimeException or an Exception, the format of the date was M/D/Y which would crash when revisiting the page after saving. Changed the format to Y-M-D.