LP#1691263: make webstaff MARC editor wrap long fields

LP#1691263: make webstaff MARC editor wrap long fields

This patch makes the MARC editor wrap long fields (e.g.,
bibliographic 505 fields) so that they fit the width of the enclosing
window or modal. The approach taken is replacing the text input
elements with contenteditable divs, which in turn can be better
styled.

To test
-------
[1] Apply the patch.
[2] Locate a record with a long 505 field and open it in the
    MARC editor. Verify that the contents of the field wrap.
[3] Verify that record editing and saving work as expected.

Signed-off-by: Cesar Velez <cesar.velez@equinoxinitiative.org>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>