Implemented addition to and removal from cart. #6409

1. Addition to cart is checked in three places -:
    * Product Page
    * Related product on a product page
    * Wishlist
2. Removal from cart has been implemented for the Delete link which appears for each product in the cart as well as the hover menu.
3. Corrected the GA callback and timeout mechanism.
4. Shifted code to single place, i.e., base.jinja.