Bug 11175: (QA follow-up) Take account of bug 15851

Bug 11175: (QA follow-up) Take account of bug 15851

We can simplify the code introduced by bug 15851 by moving the
'show_analytics_link' variable assignment into C4::XSLT and thus making
the code more DRY.

Taking the code in bug 15851 as inspiration this patch also adds proper
handling for UseControlNumber vs EasyAnalytics style 773 linking and
ensures we only return analytic component parts and no other records
containing 773's.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Andrew Nugged <nugged@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>