cinnamon-calendar-server.py: Refresh remote calendars when the event list is opened. The applet relies on evolution-data-server being aware of changes and keeping up-to-date. Unfortunately, online accounts aren't polled often unless a real client is launched (like gnome-calendar). Enable client refreshing in the cinnamon-calendar-server process and trigger it when the applet is opened. This should refresh the applet event view with any recent updates, even from remote sources. Fixes #12652.