Bug 27943: Add support for 7XX equal terms on authorities marc21 display

Bug 27943: Add support for 7XX equal terms on authorities marc21 display

Currently when a MARC21 authority has 7XX field they do not display on
authority search result page. 7XX is equal term of 1XX based on LC rules.
Applying this patch will enable that feature, which is important for non latin
catalogues.

Test plan:
1) Add a new authority with 1XX and 7XX fields.
2) Try to search that authority and check if 7XX values are displayed
3) Apply this patch
4) Try to search that authority and you will see that 7XX values are displayed
   like "1XX = 7XX"

Sponsored-by: Keratsini-Drapetsona Municipal Library, Greece
Mentored-by: Andreas Roussos
Signed-off-by: Frank Hansen <frank.hansen@ub.lu.se>
Works for me!

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>