3/22 Office Unit Testing

More unit testing for the Items class; using mocks frequently. Additional
classes for Carts and Vendors.

	modified:   api/app/controllers/BaseController.php
	new file:   api/app/models/repositories/CartRepositoryInterface.php
	new file:   api/app/models/repositories/EloquentCartRepository.php
	modified:   api/app/models/repositories/EloquentItemRepository.php
	new file:   api/app/models/repositories/EloquentVendorRepository.php
	new file:   api/app/models/repositories/VendorRepositoryInterface.php
	modified:   api/app/routes.php
	modified:   api/app/tests/TestCase.php
	modified:   api/app/tests/controllers/ItemsControllerTest.php
	new file:   api/app/tests/integration/IntegrationTest.php