deposit: loading indicator for conferences typeahead

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
deposit: fix for empty conferences suggestions

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
deposit: conferences typeahead fixes

* Fixes value reset on blur.

* Fixes  undefined value errors on keypress after a suggestion was
  chosen and the user exited the input field.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>