Send dataChanged when redo()/undo() is done.

Description

Send dataChanged when redo()/undo() is done. Otherwise it will not be done when doing undo and redo and it will be done before the command is executed if parent is set

Conformity

• Changelog entry
• Unit tests
• Update INSTALL
• Downport
• Fixes: #803 (closed)

When external dependencies are removed

• Reporting to ...