Set iCal component to proper Olson zoneinfo: Closes bgo#725777

libical could parse PST into an Olson code but choked on PDT,
bringing this problem to light.  Time zone objects now always carry
their Olson zoneinfo with them.  Also some work here to clean up
how system information is maintained (Calendar.System) and the local
time zone is now being fetched from timedated rather than relying on
GLib.TimeZone.local, which did not offer the Olson code.