Upgraded to work with cozy-ical >= 1.0 and multi-calendar support

We should wait for https://github.com/cozy/cozy-ical/pull/12 before merging this since it has been tested with the cozy-ical version in the PR.

I also added multi-calendar support.
Actually, title and organization are used to build the `prodid` (product ID) iCal attribute. "This property specifies the identifier for the product that created the iCalendar object." (see https://tools.ietf.org/html/rfc5545#section-3.7.3 for more details).

The previous "my-calendar" was a mis-usage.