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/models/setting.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+class Setting < RailsSettings::Base
+  source Rails.root.join('config/settings.yml')
+  namespace Rails.env
+
+  def to_param
+    var
+  end
+
+  class << self
+    def all_as_records
+      vars    = thing_scoped
+      records = vars.map { |r| [r.var, r] }.to_h
+
+      default_settings.each do |key, default_value|
+        next if records.key?(key) || default_value.is_a?(Hash)
+        records[key] = Setting.new(var: key, value: default_value)
+      end
+
+      records
+    end
+
+    private
+
+    def default_settings
+      return {} unless RailsSettings::Default.enabled?
+      RailsSettings::Default.instance
+    end
+  end
+end