Implement "Add to Calendar" for Repeated Events

[vsoch]

Currently, the add to calendar button can work easily for a non-repeated event because we have a reliable date and time from the event markdown directly. Repeated events are generated by the fullcalendar plugin so we don't have this, so we can't populate the javascript call. A solution to this problem would (I think) be able to associate the date from the calendar with a link to the page, possibly as a GET variable, and then have the page read it into the calendar button login. In other words, here is how I would do this:

1. Figure out how to get the actual (calculated) date time for an event, and add it to a data attribute somewhere
2. Hijack the event on click (event.preventDefault) and retrieve this value, add it to the url that would have been clicked
3. On the event page, retrieve the variable from the GET and use it to populate the add to calendar button.

Done!