countme: fix ItemWriter 'tablename' traceback
    
    I added `tablename` to `SQLiteWriter._get_writer()` so it could be used for
    writing countme_raw and countme_totals, which broke non-SQLite writers:
    
      TypeError: _get_writer() got an unexpected keyword argument 'tablename'
    
    This commit fixes the _get_writer() methods for the other classes so
    they accept/ignore `tablename` and other unexpected keyword arguments.