Refactored CartBundle

* Added more useful functional and unit tests
* Refactored managers, and uncoupling them a little bit more
* Uncoupled as much as possble all managers with ObjectManager
* Updated entity relation mapping definitions
    * Added orphanRemovals
    * Added properly all cascade definitions
* Added by default buildSchema in WebTestCase
* Fixed CartCoupon to work properly with these changes
* Added some minor tests in CartCouponBundle
* Passed php-cs-fixer