Fixed event.extendedProps object to be used as json.

Added RRule plugin:

The RRule plugin is a connector to the rrule js library. It is powerful for specifying recurring events, more so than FullCalendar’s built-in simple event recurrence.

• Updated to version 6.1.10
• Fixed some issues on RemoveAllEvents action.
• UpdateEvent client action has been removed. Now, you can use "setProp" method from event object to update the event or even refresh event by server action. See https://fullcalendar.io/docs/Event-setProp
• The module has been converted to library.
• The older FullCalendar_v5 block has been named as DEPRECATED.
• Block's image preview has been changed to smaller one.

In development: Integration with iCalendar feed.