Add widget feeds to homepage

Note there is some funkiness going on with class loadings
Had to create a `feed` and `widget_feed` table even though in this
first version the Widget::Feed includes only uses ActiveModel instead
of ActiveRecord, otherwise some specs failed

We’ll figure it out and clean up 😌

db/dev_seeds/settings.rb

@@ -63,4 +63,8 @@ section "Creating Settings" do
   Setting.create(key: 'map_longitude', value: -3.7)
   Setting.create(key: 'map_zoom', value: 10)
   Setting.create(key: 'related_content_score_threshold', value: -0.3)
+
+  Setting['feature.homepage.widgets.feeds.proposals'] = true
+  Setting['feature.homepage.widgets.feeds.debates'] = true
+  Setting['feature.homepage.widgets.feeds.processes'] = true
 end