Add dashboard saving

src/metabase/api/automagic_dashboards.clj

src/metabase/api/dashboard.clj

src/metabase/automagic_dashboards/comparison.clj

src/metabase/automagic_dashboards/filters.clj

src/metabase/automagic_dashboards/populate.clj

src/metabase/models/dashboard.clj