Enforcing IAggregateRoot (#273)

- Enforcing it on the Async and EfRepositories
- Making CatalogBrand, Item, and Type AggregateRoots because they are
just lookup tables

tests/IntegrationTests/Repositories/BasketItemRepositoryTests/DeleteAsync_Should.cs

@@ -1,46 +0,0 @@
-using Microsoft.EntityFrameworkCore;
-using Microsoft.eShopWeb.ApplicationCore.Entities.BasketAggregate;
-using Microsoft.eShopWeb.Infrastructure.Data;
-using Microsoft.eShopWeb.UnitTests.Builders;
-using System.Linq;
-using System.Threading.Tasks;
-using Xunit;
-using Xunit.Abstractions;
-
-namespace Microsoft.eShopWeb.IntegrationTests.Repositories.BasketItemRepositoryTests
-{
-    public class DeleteAsync_Should
-    {
-        private readonly CatalogContext _catalogContext;
-        private readonly EfRepository<Basket> _basketRepository;
-        private readonly EfRepository<BasketItem> _basketItemRepository;
-        private BasketBuilder BasketBuilder { get; } = new BasketBuilder();
-        private readonly ITestOutputHelper _output;
-
-        public DeleteAsync_Should(ITestOutputHelper output)
-        {
-            _output = output;
-            var dbOptions = new DbContextOptionsBuilder<CatalogContext>()
-                .UseInMemoryDatabase(databaseName: "TestCatalog")
-                .Options;
-            _catalogContext = new CatalogContext(dbOptions);
-            _basketRepository = new EfRepository<Basket>(_catalogContext);
-            _basketItemRepository = new EfRepository<BasketItem>(_catalogContext);
-        }
-
-        [Fact]
-        public async Task DeleteItemFromBasket()
-        {
-            var existingBasket = BasketBuilder.WithOneBasketItem();
-            _catalogContext.Add(existingBasket);
-            _catalogContext.SaveChanges();
-            
-            await _basketItemRepository.DeleteAsync(existingBasket.Items.FirstOrDefault());
-            _catalogContext.SaveChanges();
-
-            var basketFromDB = await _basketRepository.GetByIdAsync(BasketBuilder.BasketId);
-
-            Assert.Equal(0, basketFromDB.Items.Count);
-        }
-    }
-}