Idea Summary
To give ability for the Developers to undo their changes after saving. 

Use Case
Developers often do changes in certain page and saves their work to for testing at the runtime, if they were not satisfied with the result and they want to undo their recent changes then they just press on undo button to get back to the original code before last changes.

Preferred Solution (Optional)
To activate undo button in the app builder after saving.