Allow updating the status of notifications

You can update the same "notifications" section that we allow you to
update in "my account".

This "subscriptions" section differs from the "my account" section
because we do not need to be logged in to update the status of the
notifications.

config/routes/account.rb

@@ -2,4 +2,4 @@ resource :account, controller: "account", only: [:show, :update, :delete] do
   get :erase, on: :collection
 end
 
-resource :subscriptions, only: [:edit]
+resource :subscriptions, only: [:edit, :update]