Bug 4374 Improve biblio data entry form regarding hidden/mandatory fields

Bug 4374 Improve biblio data entry form regarding hidden/mandatory fields

Biblio framework has 3 entry points controlling if input box are
displayed by default in data entry form:

  - 'mandatory' flag at field level
  - 'mandatory' flag at subfield level
  - 'hidden' flag at subfield level

It doesn't work as it should (?):

  - All subfields are expanded (shown) if their field is mandatory
  - A subfield containing anything is always expanded whatever it contains
  - A mandatory subfield is always expanded
  - An hidden subfield isn't expanded.

Default framework having 0 in all marc_subfield_structure.hidden, by default
all subfields will be expanded.

TO BE INTEGRATED IN RELEASE NOTES:

  Koha sysadmin should have to edit its frameworks to add hidden=1 in
  appropriate subfields.

Signed-off-by: Stéphane Delaune <stephane.delaune@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>