=== ICALToHeader

ICALToHeader takes a Map of filenames to ICAL4J calendars, will pick the first Calendar,
and add it to the headers of the e-mail.

The following headers will be added : X_MEETING_UID, X_MEETING_METHOD, X_MEETING_RECURRENCE_ID, X_MEETING_SEQUENCE,
X_MEETING_DTSTAMP

The only configuration parameter for this mailet is the attribute the ICAL4J Calendar map should be attached to,
named *attribute*.

Configuration example :

....
<mailet match=??? class=ICALToHeader>
    <attribute>icalendars</attribute>
</mailet>
....