Bug 35119: Use page-section and bg-danger on biblio errors

Bug 35119: Use page-section and bg-danger on biblio errors

This patch uses the page-section and bg-danger classes to increase the
prominence of bibliographic record errors in the staff client to
encourage staff to fix such issues as soon as possible.

We also output the actual encoding error in a <pre> block to maintain
the proper whitespacing of the errors themselves.. this makes it much
clearer which characters are the issues.

Test plan
1) Using ktd navigate to record 369
2) Note the display of an encoding warning at the top of the page
3) Apply the patch
4) Refresh the above page and note the stronger visual prominence of the
   error

Signed-off-by: David Nind <david@davidnind.com>
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>