[Fix bug 761559] Implement multiple event iCal export

* Implement client side key/value url handling in events page
* Implement iCAL API serializer
* Add regex to handle events urls
* Add template to generate multiple event iCal
* Add button to export iCAL in events list
* Add test to multi event iCAL export
Merge pull request #359 from johngian/761559

[Fix bug 761559] Implement multiple event iCal export