WL-3170 Add a test for iCal method
WL-3170 Test calendar without attendees
WL-3170 Add tests for attendees without emails

If an attendee has no email address then this shouldn't break everything
WL-3170 Handle attendees without emails
WL-3170 Test can define `vevent_sequence`

We should be able to define the sequence of an event through the
"vevent_sequence" parameter.

It is used this way in signup.
WL-3170 Cancelled events have sequence

The sequence property needs to be defined on events within cancelled
calendars. We should define the sequence when constructing the event but
if we come to the point of cancelling an event which doesn't have sequence
defined then lets add it in for good measure.
Merge pull request #5 from ox-it/WL-3170

WL-3170 Generate calendars robustly