Bug 20785: Advanced Editor does not honor MarcFieldDocURL

Bug 20785: Advanced Editor does not honor MarcFieldDocURL

The advanced MARC editor, Rancor, doesn't obey MarcFieldDocURL.
Make it do so.

Test plan:

1) Enable EnableAdvancedCatalogingEditor
2) Set MarcFieldDocURL to eg. http://{MARC}.example.com/{LANG}/{FIELD}
3) Go to Cataloging -> Advanced editor
4) Go to any field and press Ctrl-H
5) Marc field documentation on www.loc.gov or ifla.org should open
6) Apply patch
7) Repeat 3 and 4. The Marc field docs should open on the URL you set

Signed-off-by: Pasi Kallinen <pasi.kallinen@joensuu.fi>
Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>