Order budget groups by id

To maintain order after editing a group’s name

We should probably add timestamps to `groups` and `headings` and order
by `created_at` instead

app/views/admin/budgets/show.html.erb

@@ -3,5 +3,5 @@
 <h2><%= @budget.name %></h2>
 
 <div id="<%= dom_id @budget %>_groups">
-  <%= render "groups", groups: @budget.groups %>
+  <%= render "groups", groups: @budget.groups.order(:id) %>
 </div>