Obsoletes umbraco.presentation.cache with new Umbraco.Core.CacheRefreshersResolver

Have removed ResolverBase as we cannot rely on manually setting the current singleton object since applications outside of the standard umbraco web application
might be using these singletons and would expect they already be setup. Have changed all current resolvers to manage their
own singleton instances and sealed them.

src/Umbraco.Web/PluginTypeResolverExtensions.cs

@@ -44,15 +44,5 @@ 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>();
-		}
 	}
 }