Make CacheHelperExtensions public so we can call CachedPartialView and ClearPartialViewCache

In order to allow extensions to the logic and usage of the CachedPartial HtmlHelper, expose CachedPartialView and ClearPartialViewCache by making the wrapping static class public.

src/Umbraco.Web/CacheHelperExtensions.cs

@@ -16,7 +16,7 @@ namespace Umbraco.Web
 	/// <summary>
 	/// Extension methods for the cache helper
 	/// </summary>
-	internal static class CacheHelperExtensions
+	public static class CacheHelperExtensions
 	{
 		/// <summary>
 		/// Application event handler to bind to events to clear the cache for the cache helper extensions
@@ -84,4 +84,4 @@ namespace Umbraco.Web
 			cacheHelper.ClearCacheByKeySearch(PartialViewCacheKey);
 		}
 	}
-}
+}