Remove items from the shopping cart if they are for a course whose course enrollment window has closed

changed the url name to verify_cart and change the color of the message in the shopping cart
Merge pull request #6124 from edx/muhhshoaib/WL-164

Unpurchased items in the shoppingcart should be removed if the enrollment period has closed
WL-105 Show course cards sorted by start dates, latest first.