Status if this appointment represents an invitation.
0: Unknown - used when initializing
1: Default value when the appointment is not a booking child
2: The invitation has been accepted
5: An invitation to a meeting not observed by the attending party
6: The meeting has been moved
7: An invitation to a meeting observed by the attending party. This can also be viewed upon as a tentative response to participate in the meeting.
8: The meeting has been moved, and this is observed by the attending party
9: The invitation has been declined/rejected
10: The meeting has been cancelled.