Standardize namespaces to all be under the Microsoft.eShopOnWeb namespace and update default namespaces. (#102)

src/ApplicationCore/Exceptions/BasketNotFoundException.cs

@@ -1,6 +1,6 @@
 using System;
 
-namespace ApplicationCore.Exceptions
+namespace Microsoft.eShopWeb.ApplicationCore.Exceptions
 {
     public class BasketNotFoundException : Exception
     {

src/ApplicationCore/Exceptions/GuardExtensions.cs

@@ -1,4 +1,4 @@
-using ApplicationCore.Exceptions;
+using Microsoft.eShopWeb.ApplicationCore.Exceptions;
 using Microsoft.eShopWeb.ApplicationCore.Entities.BasketAggregate;
 
 namespace Ardalis.GuardClauses