Expose the rangeController in ASTableView

AsyncDisplayKit/ASTableView.mm

@@ -720,6 +720,11 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
 
 #pragma mark - ASRangeControllerDataSource
 
+- (ASRangeController *)rangeController
+{
+    return _rangeController;
+}
+
 - (NSArray *)visibleNodeIndexPathsForRangeController:(ASRangeController *)rangeController
 {
   ASDisplayNodeAssertMainThread();