Extended Basket model, OrderItem and BeerShopContext.
Added functionality to basket controller: creating basket, adding and removing items. Also incrementing and decrementing of amount in basket is added, but int this commit it is not yet working (database validation exception).
Incrementing/decrementing in basket is now working.

The problem was in validation which failed if OrderItem.item wasn't loaded from DB.
Removed comments.
Basket detail is now partial view widget.
Added main Administration controller.
Added link for the administration to the layout.