Add admin layout with admin navigation

And remove the hacky link list from the dashboard.

app/controllers/admin/donations_controller.rb

@@ -1,5 +1,6 @@
 class Admin::DonationsController < Admin::BaseController
   before_action :set_donation, only: [:show, :edit, :update, :destroy]
+  before_action :set_current_section, only: [:index, :show, :new, :edit]
 
   # GET /donations
   # GET /donations.json
@@ -71,4 +72,8 @@ class Admin::DonationsController < Admin::BaseController
     def donation_params
       params.require(:donation).permit(:user_id, :amount_sats, :amount_eur, :amount_usd, :public_name, :paid_at)
     end
+
+    def set_current_section
+      @current_section = :donations
+    end
 end