WebSearch: support for 'x*' search output format
WebSearch: support for 'x*' search output format

* Ports behaviour for formating search results using output formats
  starting with 'x*'.  (addresses #1508)

* TODO refactor code to remove duplications in the websearch blueprint.

Signed-off-by: Jiri Kuncar <2bdffcb416fed3002465740d19a053a39918cbe5@cern.ch>

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