global: removal of depreated WTForms extenstion
global: removal of depreated WTForms extenstion

* Replaces Required validator with DataRequired.
  (addresses #2620)

* Fixes PEP8/257.

Signed-off-by: Leonardo Rossi <5460ec99b71a72e7693c4088b5c2585e76e1c857@cern.ch>
Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

tiborsimko/invenio-access,tiborsimko/invenio-access,inveniosoftware/invenio-access,inveniosoftware/invenio-access