馃崚 applets/digitalclock: Localize custom date format, too
Qt.formatDate with locale only accepts Locale.FormatType as format type, no Qt.DateFormat (ISODate) and no format string. Locale.toString on the other hand only formats a date with time...
Also refactor it to store a formatter function which is then used to format the date.
(cherry picked from commit f3ef11ea)