updated CCR scorer that allows excluding twitter or wikipedia entities

also, initial SSF scorer that uses a cascade of filters

data in next commit
three data files containing TREC KBA 2013 ground truth data:

  * CCR judgments expanded with more vitals inferred from SSF judgments:
      two files: before-cutoff and before-and-after-cutoff

  * SSF target events with stream_ids added by regex matching the
    strings selected by assessors.