WebSearch: guess primary collection with multi 980
WebSearch: guess primary collection with multi 980

* Allows primary collection guessing in case of multiple 980__a fields.
  (closes #545)

inveniosoftware/invenio-records,tiborsimko/invenio-records,inveniosoftware/invenio-records,tiborsimko/invenio-search,tiborsimko/invenio-records,tiborsimko/invenio-search,inveniosoftware/invenio-search,inveniosoftware/invenio-search