Undo and Redo Button Feature

[LloydBG]

The Open-LaTeX-Studio has a Undo and Redo features but these feature only works between the code changes in the working document. An improve Undo and Redo feature will allow the user to undo/redo changes within the application. For example, User opens "Document A", then the user opens another document named "Document B". The current working document is the "Document B" when the user clicks the Undo button the current working document must revert back to "Document A". While clicking the redo button will revert the current working document to "Document B"