Undo for specific operations

[maxkfranz]

Allow undo to work for specific operations that are destructive.

• Ephemeral undo: Undo should be on a per-operation basis. Each operation should store the previous state before performing the operation. The previous state can be used to perform undo.
• Undo should be available for layout: After applying a layout, the user gets the option to go back to the previous result. This may have to be time sensitive, e.g. using debounce, in order to handle changing sliders.
• Undo should be available for style: After applying a style, the user gets the option to go back to the previous result. This may have to be time sensitive, e.g. using debounce, in order to handle changing sliders.

Discussion:

• What other features should be considered for undo in future?

[mikekucera]

I'll leave this open for a hypothetical ctrl-z style undo feature that we may implement in the future. I'll open a new issue for the history feature.

[mikekucera]

History feature: #122