Send invitation mail for room changes

[brunt82]

Steps to reproduce

1. Create an appointment and add an attendee to it.
2. Attendee accepts the appointment.
3. Meeting creator (owner) changes the room of the appointment.

Expected behaviour

Nextcloud should send an e-mail about the room change as it does while changing the date or time of an appointment.

Actual behaviour

No e-mail is sent.

In my mind a room change may have the same priority like the date / time of a meeting.

[blizzz]

Does this relate to the calendar? Then, please re-open it at https://github.com/nextcloud/calendar/

[georgehrke]

@blizzz related to the Caldav server ;)

[georgehrke]

Same solution as in nextcloud/calendar#848 (comment)

Would be nice to make https://github.com/nextcloud/3rdparty/blob/master/sabre/vobject/lib/ITip/Broker.php#L69 static.
Needs to be discussed with upstream.