redo and undo for the imglab

[ShuangLiu1992]

Hi Davis, do you think you are going to add redo and undo functionality for the imglab tool anytime soon? That would be very helpful.

[davisking]

I'm not planning on it, but maybe someone will do it and submit a PR :)

[gzbykyasin]

I have implemented the undo/redo feature for imglab (Ctrl+Z and Ctrl+Y/Ctrl+Shift+Z) with a history limit(10). I will be opening a PR shortly.

[gzbykyasin]

I've submitted the PR #3143 to add this feature