Support of recurring events in calendar interface

[buddh4]

https://github.com/humhub/humhub-modules-rest/blob/master/definitions/CalendarDefinitions.php misses definitions of recurring event specific fields as:

 * @property string uid
 * @property string rrule
 * @property string recurrence_id
 * @property int parent_event_id
 * @property string exdate
 * @property string sequence

[buddh4]

Seems there where old fields included of the form class, but not of the actual entry class: 5d9e301#diff-934e23a8ae2c4555ab7c3977a6e0749f967403a9e99b8c54aee655a3a58290f7

[donni106]

supporting recurring events per API would be a great win. anyone planned anything? otherwise i am planning to implement it with my team in our API extension. i will think of an implementation that could fit for a PR here.