Bug 14658 - Split PatronSelfRegistrationBorrowerUnwantedField into two preferences...

Bug 14658 - Split PatronSelfRegistrationBorrowerUnwantedField into two preferences for creating and editing

Test plan:
  1) Make sure there is at least one field in PatronSelfRegistrationBorrowerUnwantedField.
  2) Apply patch, and update database.
  3) Check to make sure that the new system preference
     PatronSelfModificationBorrowerUnwantedField has the same value as
     PatronSelfRegistrationBorrowerUnwantedField.
  4) Verify that the same fields are hidden for self-registering a new
     borrower and edting a new one (both on the OPAC).
  5) Change PatronSelfModificationBorrowerUnwantedField, and verify that
     the two preferences correctly apply to editing vs. creating.

Signed-off-by: Michael Sauers <msauers@dospace.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>