Increase version number and deploy v1.8.8
Increase version number and deploy v1.8.8

* update extractor
* add new class PostBlockSimilarity that indicates if similarity has
  been calculated using regular or backup metric
* update config and post blocks
* move code from PostVersionList to PostBlockVersion, make pred-setter
  private in PostBlockVersion
* update test cases
* move database-related code to project db-scripts

sotorrent/so-posthistory-extractor