CalDav: Adding imported event from invitation should not send a new notification

Invitation email should start only if the user performing the operation is the organizer of the event, otherwise invitation email will be dubled.

Steps to reproduce:

1. UserA is using WebTop through Web interface, UserB has a DAV calendar configured on his iphone.
2. UserA create a new event in WebTop inviting UserB, a mail message arrive to UserB notifying the invitation.
3. UserB, on his device (iphone), click using the native email app on the invitation message received (1st one from UserA - the organizer) and then again on the invitation .ics attachment. An import window is prompted.
4. UserB chooses a DAV calendar and add the invitation event in it.
5. After sync, it checks the Web scheduler. 

Actual behaviour:

• Accepted/Imported event on UserB device is synchronized to WebTop (the event is displayed in the scheduler UI of UserB) but a new email notification is sent to UserB itself where UserB is the sender (2nd email doubled).

Expected behaviour:

• Accepted/Imported event on UserB device is synchronized to WebTop (the event is displayed in the scheduler UI of UserB) without any other notification email, UserB is not the event organizer.