deposit: subject field improvements

* Makes subject field mandatory and changes its position.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
deposit: uploader adaptation

* Adapts uploader code to new flight based uploader.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
deposit: RequiredIfFiles validator

Signed-off-by: Pedro Gaudencio <pedro.gaudencio@cern.ch>
Revert "deposit: checkbox css improvement"

This reverts commit e4b650f2dbd5ca5565be1fdcc7e184a5c2b60502.

* See https://github.com/inspirehep/inspire-next/pull/161
  Multiselect checkboxes were not visible after this commit.