kolab-util-calendar: honour configured tls variant when creating f/b (trigger) request
kolab-util-calendar: honour configured tls variant when creating f/b (trigger) request

* in kolab_util_calendar_create_http_request(), use "http://" or "https://"
  protocol for f/b (trigger) requests, depending on the tls variant configured
  for the respective source

GNOME/evolution-kolab,GNOME/evolution-kolab