Homegrown Undo/Redo stack

[matteobart]

It seems that the TextView UndoManager, doesn't seem to work great in this project. Possibly because things are being manually added, but it seems to work well, but the logic seems a bit off from a typical text editor. Maybe worth investing in our own undo/redo logic. Be sure to carefully plan out how the logic should work before starting it. This is related to issue: #13

This would involve intercepting all changes to the TextView, including over writing keybindings (paste, undo, redo, cut).

Some reading: https://en.wikipedia.org/wiki/Memento_pattern