#20 - Upgraded to Salespoint 6.0 GA.

Upgrade to benefit from improved API of Cart as well as security improvements.
#23 - Improve CartController to use new Cart API.

CartController now introduces the new Cart API about to be released with Salespoint 6.0 GA. We also moved to the Spring MVC way of working with the session. The cart.html template now also uses the price attribute of the object instance.

We now also generally allow authenticated users to use the CartController. Previously, other authenticated roles except ROLE_CUSTOMER (e.g. the boss user) had been denied access to it.

Related pull request: #24.