Simple Gantt chart

This example shows tree structure, with freedom for levels.
When row does not contain any (not deleted) children it is standard task and its data can be changed.
When row contains some (not deleted) children it is computed group task and shows summary of its children.
The rows can be added, deleted, moved and copied and the tasks become standard or group tasks accordingly.
Selected rows can be copied to clipboard by Ctrl+C. The rows can be added by pasting from clipboard by Ctrl+V. If some rows are selected, they are replaced by pasted rows.