Rendering settings Undo/Redo

This PR adds Undo/Redo functionality to the rendering settings.

To test (preview panel and/or full image viewer):
Modify some rendering parameters without saving them, and move backwards and forwards in the "history" with the Undo and Redo buttons. Saving the settings should clear the history, i. e. Undo/Redo get disabled. After undoing until the primarily settings are reached, the save button should be disabled.


`enum`s have more type safety