oc-calendar: Extract time zone from TimeZoneDefinition

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.

OpenChange/iCalTimeZone+MAPIStore.h

@@ -30,6 +30,9 @@
 - (struct Binary_r *) asTimeZoneStructInMemCtx: (TALLOC_CTX *) memCtx;
 - (struct Binary_r *) asZoneTimeDefinitionWithFlags: (enum TZRuleFlag) flags
                                            inMemCtx: (TALLOC_CTX *) memCtx;
+- (iCalTimeZone *) iCalTimeZoneFromDefinition: (NSData *) value
+                              withDescription: (NSString *) description
+                                     inMemCtx: (TALLOC_CTX *) memCtx;
 
 @end