Fixes: #U4-2041, #U4-2040 - user cache is not invalidated when permissions change across LB environments, also streamlined how caching is handled in

these classes which now use the standardized events way to do things. Fixes a performance issue and ensures that the cache is not invalidated for 'micro'
operations during permission changes.

src/Umbraco.Web/Cache/DistributedCacheExtensions.cs

@@ -22,6 +22,11 @@ namespace Umbraco.Web.Cache
         public static void RefreshUserCache(this DistributedCache dc, int userId)
         {
             dc.Refresh(new Guid(DistributedCache.UserCacheRefresherId), userId);
+        }
+
+        public static void RefreshAllUserCache(this DistributedCache dc)
+        {
+            dc.RefreshAll(new Guid(DistributedCache.UserCacheRefresherId));
         } 
         #endregion