Implement logout and shopping cart API

- Add unique name constraint to product Categories
- Add query to locate shopping cart item by userId and productId
- Add ShoppingCart methods to remove and add items
- Add methods to User for manipulating the shopping cart (add, remove, empty..)
- Change all product methods to use integer for product id parameters
- Add rest method to logout {HOST}/rest/user/logout
- Add additional base service exception methods (unauthorized and internal error)
- Implement all shopping cart methods in ShoppingServiceImpl
- Removed CartGET and ShoppingCartContentsJSON classes
  - These methods have been implemented in ShoppingServiceImpl respectively