This class creates the popup menu, that opens when clicking onto the treeview.
Append a new node to the selected Hash or Array.
Change the type or content of the selected node.
Recursively collapse/expand a subtree starting from the selected node.
Copy the selected node and its subtree, and save it into the clipboard.
Create the menu.
Cut the selected node and its subtree, and save it into the clipboard.
Insert a new node into an Array before the selected element.
Paste the data in the clipboard into the selected Array or Hash by appending it.
Paste the data in the clipboard into the selected Array inserting it before the selected element.
[Validate]