Add a set of modes to the task panel with buttons to switch among them in the panel's title bar.
Add a "select" mode to rubber-band select a set of tasks.
Add a "connect" mode to insert arcs (dependencies and/or adaptors) into the task graph. This inserts a qtPreviewArc item into the task-panel's scene that illustrates a potential connection as users click on tasks.
Implement an AddDependency operation that inserts a dependency arc.