[betaseries_list] add a plugin for querying the series from www.betaseri...

...es.com

The plugin is meant to work with the import_series plugin as follow:

        import_series:
          from:
            betaseries_list:
              username: xxxxx
              password: xxxxx
              api_key: xxxxx

Api key can be requested at http://www.betaseries.com/api.