handle vcalander documents with recurrence with exemptions or edits

when importing ics files from third party services (ex: google), long
running recurrence vcalander objects can contain numerous vevents
relating to past exemptions or edits.

these objects are handled incorrectly, leading to incorrect first and/or
last occurence dates from being inferred. as a result, a number of
imported events are not rendered in the calendar.

this PR makes use of EventIterator's constructor that takes in an array
of VEVENTS to properly handle these complex cases.

Also of note is that other parameter signatures of EventIterator's constructor,
will be deprecated, according to comments in sabre dav EventIterator.php

Signed-off-by: leith abdulla <online-nextcloud@eleith.com>