handle destroy layout

app/models/layout.rb

@@ -6,6 +6,8 @@ class Layout
    key :description, String
    key_i18n :content, String
    
+   many :children, :class_name => "Item", :foreign_key => "layout_id", :dependent => :nullify
+   
    validates_format_of :name, :with => /^[a-zA-Z-_]+$/
    
 end