Add undo/redo functionality

[jaggedjimmyj]

First of all, thank you for the great product! Just used it to print 20+ labels, and I can say that it is very good already.

However, one of the biggest gripes that I had using it, is the lack of undo/redo functionality. Would love to see it implemented in the future versions.

[MultiMote]

Thank you for your kind words!

This functionality isn't usually easy to implement, but I'll give it a try someday.
Added to Roadmap.