deposit: separation of typeahead initialization

• Separates connecting events and initializing typeahead so that one can set up a custom typeahead with all the events connected with the form. (closes #2442)

Co-authored-by: Kamil Neczaj <kamil.neczaj@cern.ch>
Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>