Bug 36370: Add ContentWarningField to UNIMARC XSLT

Bug 36370: Add ContentWarningField to UNIMARC XSLT

Bug 31123 added new feature with preference ContentWarningField.
Add this behavior to UNMARC XSLT files.

This patch adds new template 'tag_content_warning' in UNIMARCslimUtils.xsl
called in results and details pages.

New field is placed after 3xx.

Test plan (in both interfaces OPAC and staff):
1) Create a new field 599 in framework
2) Set system preference ContentWarningField to 599
3) Edit a record to add a 599 with text in $a$b and an URL in $u
4) Perform a search to find this record
=> Check you see content_warning: <a href="$u">$a</a> $b
5) Click on details page
=> Check you see content_warning: <a href="$u">$a</a> $b

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>