OAIHarvest: do filtering first (OPS)

* Filters first and ignores updates for extraction of plots, fulltext
  authors, references etc.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Merge pull request #149 from jalavik/oaiharvest-refactor-steps

OAIHarvest: do filtering first (OPS)