Bug 8210: add links to authorities to headings in OPAC

Bug 8210: add links to authorities to headings in OPAC

At the moment, there is no way to get to an authority record from a bib
record that uses it other than doing a new search on the authority file.
This patch adds a link (a cute little magnifying glass) to linked
authority records on the OPAC detail view for MARC21 and NORMARC
with XSLT enabled. A follow-up patch will add the link to regular mode.
Because UNIMARC handles authorities differently, the link is not added
to the XSLT.

Test plan:
1) Set OPACXSLTDetailsDisplay to 'default'
2) View a record that has some headings that are linked to authority
   records in the OPAC (easiest way to find a record like that is to
   edit a record and add some headings using the thesaurus plugin)
3) Observe the cute little magnifying glass links to the authority.

Revised version of the patch adds a space between the heading and the
magnifying glass.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Patch works nicely.

If a library does not like to see the
magnifying glass/link to the authority, it's easy to disable it
by adding the line .authlink {display:none;} to OpacUserCSS.