added localstrorage into index_shopping_cart.html.erb

在商品显示页面中加入了localstrorage，点击加入购物车，添加localstrorage，在购物车页面中取出localstrorage显示商品信息，并修复了购物车页面的价格显示，保留小数点两位。
added animate to input-shoppingcart botton from show_product.html.erb

 给加入购物车按钮加入了购物车动画
added localstrorage and animate to show_product.html.erb