changes all instances accessing cache by key "contentItem" to use CacheKeys.ContentItemCache and replaces

all of it's cache usages with the ApplicationContext.Current.ApplicationCache. Obsoletes a couple of methods
that are not used.

src/Umbraco.Core/Cache/HttpRuntimeCacheProvider.cs

@@ -277,6 +277,20 @@ namespace Umbraco.Core.Cache
             return result.TryConvertTo<TT>().Result;
         }
 
+        /// <summary>
+        /// Inserts an item into the cache, if it already exists in the cache it will be replaced
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="cacheKey"></param>
+        /// <param name="priority"></param>
+        /// <param name="getCacheItem"></param>
+        public override void InsertCacheItem<T>(string cacheKey,
+                                                CacheItemPriority priority,
+                                                Func<T> getCacheItem)
+        {
+            InsertCacheItem(cacheKey, priority, null, null, null, getCacheItem);
+        }
+
         /// <summary>
         /// Inserts an item into the cache, if it already exists in the cache it will be replaced
         /// </summary>