WebSearch: fix collection order on the search page
WebSearch: fix collection order on the search page

* Collection list on the search page should follow the same order
  of sub-collections as they appeared on the starting collection
  splash page from where the given search originated. (closes #900)

* Cherry-picked from 8ef26dd58830455e09a6e10331e12d91b9c7f494.

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