Improve relayout when constrained size of all nodes is changed:

- In -layoutSubviews of table and collection views, detect changes that cause a different constrained size for nodes, and trigger relayout immediately.
- Orientation change can be handled by this solution. So, no need to observe to its events.
- Update Kittens example to support iPad (easier to catch bugs on these devices) and add a title to navigation bar (looks a bit nicer).

examples/Kittens/Sample/ViewController.m

@@ -59,6 +59,7 @@ static const NSInteger kMaxLitterSize = 100;        // max number of kitten cell
 
   _blurbNodeIndexPath = [NSIndexPath indexPathForItem:0 inSection:0];
   
+  self.title = @"Kittens";
   self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemEdit
                                                                                          target:self
                                                                                          action:@selector(toggleEditingMode)];