vCal export support

[sander]

For internal company use, a feature request is to support sending a final vCal invitation file to invitees.

http://en.wikipedia.org/wiki/VCal

A patch is being worked on. My advice to the author:

I think you'll need to create a new 'admin tool' in the appointment overview. There the initiator is instructed to select one of the dates in the table above. Pushing the button should send a POST request to a new view named plapp.views.send_vcal. That view can just output the vCal file using a Django template.

Correction: the person who wanted to write this patch decided to implement HTA export support instead.