LP#921142: Bring back automatic padding of short fixed fields in the GUI MARC editor

Bring back automatic padding of short fixed fields in the GUI MARC
editor. Also, use onblur instead of oninput, so that we've already lost
focus and don't care if that happens again.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Remington Steed <rjs7@calvin.edu>
Signed-off-by: Ben Shum <bshum@biblio.org>