[Development] Moving QUndoStack and QUndoCommand out of QtWidgets

[Jesus Sanchez-Palencia]

Hi there,

I would like to gather your opinion on whether we should move
QUndoStack and QUndoCommand out of QtWidgets so they could be used
without requiring this module as an extra dependency.

After a brief investigation, I believe this could done by:

1- moving QUndoCommand entirely;

2- moving QUndoStack without moving the APIs that rely on or need
QAction (QAction *createUndoAction() and QAction *createRedoAction());

3- creating a new class (QUndoStackAction ??) inside QtWidgets and
implement the APIs mentioned above there (createUndoAction and
createRedoAction);

4- applying the same logic to QUndoGroup.


QtWebKit, for instance, would benefit from this immediately, as we aim
on removing the QtWidgets dependencies.

Suggestions, comments and any sort of feedback here would be more than welcome.

Thanks in advance,
Jesus Sanchez-Palencia