BibRank: run citation indexer after word indexer
BibRank: run citation indexer after word indexer

* Checks indexing times of `journal' and `reportnumber` indexes
  and compares against the latest record modification timestamp
  in the system, because if these indexes are not up to date yet,
  then we should wait and not run incremental citation indexing
  as of yet.  Let us wait for the next wake-up of the citation
  indexer daemon in this case.  (closes #918)

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