WebStyle: legacy request form multivalue fix
WebStyle: legacy request form multivalue fix

* Addresses general problem with reading multiple POST arguments of same
  name as list.

Reported-by: Raquel Jimenez Encinar <61e1365c63f21567aa203999820482535e76d1b4@cern.ch>
Signed-off-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

tiborsimko/invenio-base,tiborsimko/invenio-base,inveniosoftware/invenio-base,inveniosoftware/invenio-base