Stable1.5 backports 1.5.8 (#760)

* fix parsing all-day events with DTSTART only

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

* fix handling of events with recurrence exceptions only

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

* Escape calendar sharing drop down.

* Escape attendees

* Escape locations