created item groups and link banners and their associations and fixed bugs with join tables

back-office/app/models/item.rb

@@ -3,7 +3,7 @@ class Item < ActiveRecord::Base
   has_many :multi_media_descriptions
   belongs_to :sub_category
   belongs_to :supplier
-  belongs_to :special_offer
+  has_and_belongs_to_many :item_groups, :join_table => 'item_item_groups'
 
   validates_presence_of :name, :description, :list_price, :current_input_price, :tags, :unit_id, :code, :sub_category_id, :weight, :supplier_id