Implement the command pattern for modifying charts

[Kangaroux]

📖 Overview

For the undo/redo feature we need a history of user modifications. Encapsulating them with the command pattern would be best.

These actions should be separate from the Gtk actions. We don't need all the extra functionality of Gtk actions. If there are actions we need to trigger from the menu we can do so by creating a Gtk action that calls these.

public interface IUserAction
{
 void Apply();
 void Revert();
}