Support multiple dashboards

[macbre]

An example for example.yaml config file:

# now features "score" will be calculated using the metrics defined above with per-feature parameters set
features:
    - name: PanTadeusz
      url: "http://lubimyczytac.pl/ksiazka/4871036/pan-tadeusz"
      template:
        book_id: 4871036
      metrics:
        # additional metric just for this book
        - name: lubimy_czytac/wants_to_read

    - name: "Wojna i Pókój"
      url: "http://lubimyczytac.pl/ksiazka/4869384/wojna-i-pokoj-tom-1"
      template:
        book_id: 4869384

# define customised dashboards, the one under the root URL will display all features
dashboards:
   - name: "Literatura Polska"
     features:
       -  PanTadeusz