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

app/lib/hash_object.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class HashObject
+  def initialize(hash)
+    hash.each do |k, v|
+      instance_variable_set("@#{k}", v)
+      self.class.send(:define_method, k, proc { instance_variable_get("@#{k}") })
+    end
+  end
+end