Created RepositoryInstanceResolver/Factory to replace the configuration based instantiation of Repo's.

Added unit tests to support resoling each instance, fixed CodeFirstTests to ensure that the base.TearDown() method is
called. Changed the BaseMapper's to internal.

src/Umbraco.Tests/CodeFirst/CodeFirstTests.cs

@@ -228,8 +228,11 @@ namespace Umbraco.Tests.CodeFirst
         [TearDown]
         public override void TearDown()
         {
+			
             DatabaseContext.Database.Dispose();
 
+			base.TearDown();
+
             //reset the app context
             DataTypesResolver.Reset();
             ApplicationContext.Current = null;