deposit: proceedings info box additions

* Adds nonpublic_note field (500__a) to Proceedings Info Box.

* Disables Proceedings Box if any journal information is filled.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Co-authored-by Georgios Kokosioulis <georgios.kokosioulis@cern.ch>