item groups now have order - start page is now item group 1 (configurable in globals)

back-office/app/models/item_in_group.rb

@@ -0,0 +1,8 @@
+class ItemInGroup < ActiveRecord::Base
+	belongs_to :item_group
+	belongs_to :item
+
+	validates_presence_of :item_group_id
+	validates_presence_of :item_id
+	validates_presence_of :position
+end