Added delete and redownload commands to History Grid (redownload will delete the existing item from history and then start an episode search)

NzbDrone.Core/Providers/HistoryProvider.cs

@@ -63,5 +63,10 @@ namespace NzbDrone.Core.Providers
 
             return history.FirstOrDefault();
         }
+
+        public virtual void Delete(int historyId)
+        {
+            _database.Delete<History>(historyId);
+        }
     }
 }