Migrate from ledermann/rails-settings to rails-settings-cached which allows global settings

with YAML-defined defaults. Add admin page for editing global settings. Add "site_description"
setting that would show as a paragraph on the frontpage

config/routes.rb

@@ -58,6 +58,7 @@ Rails.application.routes.draw do
   namespace :admin do
     resources :pubsubhubbub, only: [:index]
     resources :domain_blocks, only: [:index, :create]
+    resources :settings, only: [:index, :update]
 
     resources :accounts, only: [:index, :show, :update] do
       member do