Updated how mappers for persistence work with the MapperFor attribute and have made BaseMapper public but have

kept all properties, etc.. internal just so that they can be found so we don't have to register them.
Updates unit test to ensure the plugin manager is init'd properly with the 'false' override. Ensures that the base
db test also initializes the plugin manager properly.

src/Umbraco.Tests/TestHelpers/BaseUsingSqlCeSyntax.cs

@@ -1,4 +1,7 @@
 using NUnit.Framework;
+using Umbraco.Core;
+using Umbraco.Core.ObjectResolution;
+using Umbraco.Core.Persistence.Mappers;
 using Umbraco.Core.Persistence.SqlSyntax;
 
 namespace Umbraco.Tests.TestHelpers
@@ -10,7 +13,31 @@ namespace Umbraco.Tests.TestHelpers
         public virtual void Initialize()
         {
             SqlSyntaxContext.SqlSyntaxProvider = SqlCeSyntax.Provider;
+            PluginManager.Current = new PluginManager(false);
+            MappingResolver.Current = new MappingResolver(
+                () => PluginManager.Current.ResolveAssignedMapperTypes());
 
+            //MappingResolver.Current = new MappingResolver(
+            //    new[]
+            //        {
+            //            typeof(ContentMapper), 
+            //            typeof(ContentTypeMapper),
+            //            typeof(DataTypeDefinitionMapper),
+            //            typeof(DictionaryMapper),
+            //            typeof(DictionaryTranslationMapper),
+            //            typeof(LanguageMapper),
+            //            typeof(MediaMapper),
+            //            typeof(MediaTypeMapper),
+            //            typeof(PropertyGroupMapper),
+            //            typeof(PropertyMapper),
+            //            typeof(PropertyTypeMapper),
+            //            typeof(RelationMapper),
+            //            typeof(RelationTypeMapper),
+            //            typeof(ServerRegistrationMapper),
+            //            typeof(UserMapper),
+            //            typeof(UserTypeMapper)
+            //        });
+            Resolution.Freeze();
             SetUp();
         }
 
@@ -20,7 +47,9 @@ namespace Umbraco.Tests.TestHelpers
         [TearDown]
         public virtual void TearDown()
         {
+            MappingResolver.Reset();
             SqlSyntaxContext.SqlSyntaxProvider = null;
+            PluginManager.Current = null;
         }
     }
 }