Administrators are regular users too D:
Show links to shopping cart and product admin panel if the currently logged in user has access (refs #92, refs #32)
Changes: (refs #32 (Database functions), refs #92 (Shopping Cart))

* Updated stored procedures relating to shopping carts
* Removed `CartId` from `ShoppingCart`, and instead made `UserId` and `ProductId` a composite key for each row.
* Added test data for shopping carts
Started on framework for shopping cart (refs #92)