Undo/redo

[loicknuchel]

Let's implement an undo/redo algorithm :tada:

Two buttons should be added in the command bar (bottom right), and keyboard shortcuts should be ctrl+z for undo and ctrl+maj+z for redo. Use: https://package.elm-lang.org/packages/elm-community/undo-redo/latest

If you see any other shortcut that could trigger an undo or redo, let's comment here ;) If you want this feature, please leave a :+1: reaction on this issue.