[ASCellNode] Added indexPath property. (#2468)

* [ASCellNode] Added indexPath property.

* [ASCellNode] Cached the type of scrollView we're using in the node, and placed that logic in setScrollView.

* [ASCellNode] Removed table and collection view from indexPath, since they return the index paths from the view-space.

* Changed the logic for getting indexPath so that it works even when the cell is not displayed.

* [VerticalWithinHorizontalScrolling] Explicitally synthesized indexPath property.

examples/VerticalWithinHorizontalScrolling/Sample/RandomCoreGraphicsNode.m

@@ -22,6 +22,8 @@
 
 @implementation RandomCoreGraphicsNode
 
+@synthesize indexPath=_indexPath;
+
 + (UIColor *)randomColor
 {
   CGFloat hue = ( arc4random() % 256 / 256.0 );  //  0.0 to 1.0