- TreePanel is direct descendant of the Panel class. 
	The reason - is convenience: top and bottom ToolBars, footer button bar...
	- It isn't used to contain any children except those it was designed for.
	- Like the EditorGrid, TreePanels can be configured to allow th edit data, but
	don't have a DataWriter equivalent (we must code Ajax.requests for CRUD actions)
	- Ext.data classes don't apply to TreePanels; thus Proxies and Readers are
	out of the picture. This means that the data must come either from memory or remotely
	but is limited to the same domain.