Add UNDO and REDO

[TobiasKnauss]

I really miss an UNDO button so much! You sometimes cropped an image wrongly, or automatic rotation did not work correctly. You need to scan the whole image again if you didn't save it before editing.

Describe the solution you'd like Add UNDO and REDO buttons to the page editing window, and maybe to the main window (for multi-page editing)

[cyanfish]

You can Ctrl+Z or Right Click->Undo in the main window. Also Image->Reset will reset the selected images to the state after scanning.