deposit: fix proceedings box display

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
deposit: show/hide form elements and panels

* Adds logic on the dropdown to show/hide form elements
  and panels depending on the state of dropdown and the
  related classes attached to the them.

Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>