communities: deprecated WTForms validator removal
communities: deprecated WTForms validator removal

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

* Fixes PEP8.

Signed-off-by: Adrian Pawel Baran <3f0d95b8f073876984c6beaffa367600a8350ef3@cern.ch>
Reviewed-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

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