Topology Modeler: Undo/redo actions

[miwurster]

Currently, it is not possible to undoan action in the Topology Modeler. This creates an issue e.g. when a user accidentally drags an element or assigns wrong values in the properties. It would be good to have an undo implemented either as a separate button in the top menu or with the (Ctrl + Z) shortcuts. Similarly, the redo feature is also good to have.

Source: https://github.com/radon-h2020/radon-gmt/issues/48