indexer: changes in data model

* Changes 'term' field inside IdxPHRASExxF classes
  from String to Text.

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Co-authored-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Merge pull request #17 from gszpura/pu-indexer-1

indexer: changes in data model