Bug 29529: Fix \n in hint on Koha to MARC mappings

Bug 29529: Fix \n in hint on Koha to MARC mappings

This patch breaks up a translatable string so that "\n" is excluded from
what is translated.

Unrelated: Capitalization is corrected on an instance of the phrase
"Koha to MARC Mappings."

To test, apply the patch and go to Administration -> Koha to MARC
mapping.

- The breadcrumb for the current page should have correct capitalization
  ("mapping" instead of "Mapping").
- Click the "Add" button for any Koha field. The dialog should display
  correctly:

  Adding a mapping for: biblio.abstract.
  Please enter field tag and subfield code, separated by a comma. (For
  control fields: add '@' as subfield code.)
  The change will be applied immediately.

Test the way the po file is updated:

 > cd misc/translator
 > perl translate update en-GB (for example)
 - Open the updated po file, en-GB-staff-prog.po
 - You should find these lines:

 SCRIPT
 koha-tmpl/intranet-tmpl/prog/en/modules/admin/koha2marclinks.tt:86
 msgid "The change will be applied immediately."
 msgstr ""

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>