events: hide events on the next day, such that events in progress are still shown.
events: adding last-seen activities.

trello: https://trello.com/c/cOa9EpLf/677-veranstaltungen
events#show: adding activator to the contact_people field.

Otherwise, the field can’t be edited, since the box has no ‚edit‘
button.

trello: https://trello.com/c/cOa9EpLf/677-veranstaltungen
events: adding organizer to ical format.

* gem: https://github.com/icalendar/icalendar
* format: http://tools.ietf.org/html/rfc5545#section-3.8.4.2
* trello: https://trello.com/c/cOa9EpLf/677-veranstaltungen