Merge pull request #242 in ZP/z-push from feature/ZP-835-istatemachine-cleanstates-should-get to develop

* commit '1ad4e7c8':
  ZP-835 Added new parameter to the IStateMachine->CleanStates() that indicates if only the defined counter should be deleted, implemented new flag in file state machine and sql state machine, introduced Sql->returnNullified() to nullify false keys and Sql->getSQLOp() to have the operator determination at one place, added logging to the file->db migration script, changed ZPushAdmin->RemoveDevice() to use the new flag, Utils::PrintAsString() understands "null" now.