Bug 10561: Rephrase DisplayOPACiconsXSLT and DisplayIconsXSLT slightly

Bug 10561: Rephrase DisplayOPACiconsXSLT and DisplayIconsXSLT slightly

As the pref removes the whole 'line' of information, this tries to makes
the behaviour a little clearer by adding a 'and descriptions' to the pref
text. It now reads:

[Show|Don't show]  the format, audience, and material type icons and
descriptions in XSLT MARC21 results and detail pages in ...

To test:
- Check both preference descriptions in the staff client
- Verify the text reads correctly and this helps things

Signed-off-by: David Roberts <david@koha-ptfs.co.uk>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>