Updated cache refresher factory to use PluginTypeResolver and added unit tests to show that it

resolves the objects, fixes up the GetAll() call since I'm not sure if that actually ever worked.

src/Umbraco.Web/PluginTypeResolverExtensions.cs

@@ -44,5 +44,15 @@ namespace Umbraco.Web
 		{
 			return resolver.ResolveAttributedTypes<XsltExtensionAttribute>();
 		}
+
+		/// <summary>
+		/// Returns all classes attributed with XsltExtensionAttribute attribute
+		/// </summary>
+		/// <param name="resolver"></param>
+		/// <returns></returns>
+		internal static IEnumerable<Type> ResolveCacheRefreshers(this PluginTypeResolver resolver)
+		{
+			return resolver.ResolveTypes<ICacheRefresher>();
+		}
 	}
 }