[fix bug 848756] Fixed celery deprecation warning.
Merge pull request #385 from akatsoulas/848756

[fix bug 848756] Fixed celery deprecation warning.
[fix bug 856278] Fixed typo in mozillian's event attendance.
Merge pull request #386 from akatsoulas/856278

[fix bug 856278] Fixed typo in mozillian's event attendance.
[Fix bug 858479] Set cache headers in single event iCal export