* Fixed an issue where accepting events from an external organizer would send emails
to the all event attendees upon synchronization.
* Corrected the data model for events where multiple Odoo users are attendees for the
same event. Now, only one event is created in Odoo, with all the attendees on the
same event. This conforms to Odoo's existing calendar event data model.
* Updated the setting of the organizer field (user_id) on the calendar events upon
synchronization. Previously, the organizer field was always set to the current user
whose events were being synchronized. Now, it is set based on the ORGANIZER parameter
of the iCalendar event, if present. If not present, it defaults to the current synchronizing
user. In the case that the organizer is external, the user_id field is left blank.
