Bug 35119: (follow-up) Same treatment for editor page

Bug 35119: (follow-up) Same treatment for editor page

We pushed 34014 before I thought about these changes.. I think this is a
solid follow-up to add the same styling to the catalogue editor page..
swapping the existing dialog alert with a page-section bg-danger and
thus allowing more space to 'pre' wrap the encoding error itself to ease
the spotting of errant characters.

Signed-off-by: Phil Ringnalda <phil@chetcolibrary.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>