If there are only one conference in the future and it has a public splashpage, redirect to it in conferences#index.

Change tests root_path to conference_path(conference).

fix #1259

spec/features/user_ability_spec.rb

@@ -14,7 +14,7 @@ feature 'Has correct abilities' do
     scenario 'for administration views' do
       visit admin_conference_path(conference.short_title)
 
-      expect(current_path).to eq root_path
+      expect(current_path).to eq conference_path(conference)
       expect(flash).to eq 'You are not authorized to access this page.'
     end
   end