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/seeds.rb

@@ -125,3 +125,8 @@ Setting['map_zoom'] = 10
 Setting['related_content_score_threshold'] = -0.3
 
 Setting["feature.user.skip_verification"] = 'true'
+
+Setting['feature.homepage.widgets.feeds.proposals'] = true
+Setting['feature.homepage.widgets.feeds.debates'] = true
+Setting['feature.homepage.widgets.feeds.processes'] = true
+