base layout on id instead of name

app/views/admin/pages/_form.html.erb

@@ -19,8 +19,8 @@
 <% end %>
 
 <p>
-<%= f.label :layout_name, t('admin.layout_name') %>
-<%= f.select :layout_name, Layout.all.map{ |l| [l.description, l.name] } %>
+<%= f.label :layout_id, t('admin.layout_name') %>
+<%= f.select :layout_id, Layout.all.map{ |l| [l.description, l.id] } %>
 </p>
 
 <p>