0011232: support ATTENDEE in OSX 10.10

0011232: support ATTENDEE in OSX 10.10

* In yosemite iCal adds organiser with role "chair" but has no roles for
other attendee
* In mavericks iCal adds organiser as attendee without role

https://forge.tine20.org/view.php?id=11232

Change-Id: Ie645a6a574ef9c94fa0803333e25f3c89835a432
Reviewed-on: http://gerrit.tine20.com/customers/2108
Reviewed-by: Philipp Schüle <p.schuele@metaways.de>
Tested-by: Philipp Schüle <p.schuele@metaways.de>
Reviewed-on: http://gerrit.tine20.com/customers/2904
Tested-by: Jenkins CI (http://ci.tine20.com/)