A feature request (3/4): allow the stickers to expand "fullscreen"

[thread13]

Since apparently this project had some recent attention -- I wonder if it would be possible to backport some nice features from other forks. This feature provides an alternative to #146 -- and could be possibly combined with it.

The idea is that each sticker gets "expand/undo" buttons, so that the user can make the sticker window much wider, and add or read some text that would be visible only there.

A reference implementation: stevemoreau/scrumblr.