Settings: update time zone strings on date change

If the user changes the date, most obvious case being from 1970, to a
current date, and the user's selected Locale's country time zones have
been changed (according to ICU), we must update the time zone strings in
the system.

Ref: CYNGNOS-453

Change-Id: I82cc86ae68f3fcbb6fdfc525a102ad8ae692e978
Signed-off-by: Roman Birg <roman@cyngn.com>