Substantially improve behavior of nested Table & Collection Nodes

This ensures memory cleanup happens correctly and introduces a new test project
to support developing new features while stressing tough use cases for correctness.

AsyncDisplayKit/ASTableView.h

@@ -260,6 +260,20 @@
  */
 @property (nonatomic) BOOL automaticallyAdjustsContentOffset;
 
+/**
+ * Triggers all loaded ASCellNodes to destroy displayed contents (freeing a lot of memory).
+ *
+ * @discussion This method should only be called by ASTableNode.  To be removed in a later release.
+ */
+- (void)clearContents;
+
+/**
+ * Triggers all loaded ASCellNodes to purge any data fetched from the network or disk (freeing memory).
+ *
+ * @discussion This method should only be called by ASTableNode.  To be removed in a later release.
+ */
+- (void)clearFetchedData;
+
 @end