If the event was created by the MAPI client, the client's time zone (if
present) is assigned to the event's calendar in iCalEvent+MAPIStore.
This way, we can use it to deliver the event's properties correctly.
All-day and recurrent events have a binary property that describes the
time zone they take place in. We were using the user's time zone in
the webmail, but it may not be equal to the one in the client. This
difference eventually leads to time shifts in events.
According to [MS-OXICAL] Section 2.1.3.1.1.20.13, the EXDATE property
must be written only if there are ocurrences from the series that have
been deleted and before this commit ModifiedInstanceDates were also
included.
We check against every ExceptionInfo from exception ocurrences of the series
to know if the ocurrence was deleted or only modified.
