renamed DataModel event
Moved abstract methods from data model classes to a new Decorator interface
Refactored ViewModel
Improved Tooltip implementation

Now there is only one tooltip html element per treemap instance.
Renamed Attachable property 'container' to 'shell'
Moved responsibility for branch color to Decorator class
Removed default center alignment of branch node label
Renamed Decorator.defineColor(..) to Decorator.defineNodeColor(..)
Added custom model example