let plugins define their own foodcoop-config defaults

lib/foodsoft_messages/app/overrides/admin/configs/_tab_messages/add_config.html.haml.deface

@@ -1,4 +1,4 @@
-/ insert_bottom ':root'
+/ insert_bottom ':root:last-child'
 = config_use_heading form, :use_messages, label: 'Messages' do
   = config_input form, :mailing_list, as: :string, input_html: {class: 'input-xlarge'}
   = config_input form, :mailing_list_subscribe, as: :string, input_html: {class: 'input-xlarge'}

lib/foodsoft_messages/lib/foodsoft_messages/engine.rb

@@ -11,5 +11,9 @@ module FoodsoftMessages
         sub_nav.items.insert(i, sub_nav.items.delete_at(-1))
       end
     end
+
+    def default_foodsoft_config(cfg)
+      cfg[:use_messages] = true
+    end
   end
 end