added shopping cart model 

git-svn-id: https://shopizer.svn.sourceforge.net/svnroot/shopizer/shopizer-portlet@1557 e80ee2c7-76f3-4005-aeaf-98396743f455
Added item number filed to help in sorting items list in the Shopping cart

git-svn-id: https://shopizer.svn.sourceforge.net/svnroot/shopizer/shopizer-portlet@1558 e80ee2c7-76f3-4005-aeaf-98396743f455