Bug 21058: Added HTML classes in MARC21slim2_Detail.xsl

Bug 21058: Added HTML classes in MARC21slim2_Detail.xsl

This is a very small patch. I've simply added the following classes to
their respective spans in the detail XSLs for both interfaces.

- in_note (773$n)
- preceeding_entry_note (780$n)
- succeeding_entry_note (785$n)

To test:

1. Apply patch
2. Open details page of notice with a 773$n, 780$n or 785$n field
3. Inspect element. The class should be visible.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit b65fc8e176f600894a98be526922f05e9d4f000d)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>