Honor locale time settings in lock screen.

The time display in the lock screen should honor the LC_TIME variable,
including the locale-specific settings for whether to display a 12-hour or
24-hour time.  Sending the time and date strings through gettext results in
a value which is specific to LC_MESSAGES, which can be different from
LC_TIME.  Use the %X and %x values for a time and date, which are guaranteed
to be appropriate for the locale in question.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>