deposit: field messages fix
deposit: field messages fix

* Fixes field info/warning/error/success messages, according to
  Bootstrap's newest documentation; also, adds a variable that prepares
  for future changes on the 'error' field name.

Signed-off-by: Pedro Gaudêncio <4ac9fc3191981fa13218c244381da17a72546105@cern.ch>
Reviewed-by: Javier Martin Montull <ea6b80e26c65acc242d8916fb6eefa01b123cb69@cern.ch>

tiborsimko/invenio,tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio