Undo button

Today I accidentally clicked the batch “master” on a certain page in the “manage collection” search screen of one of my custom collections, for which each of the 20 sentences on that page was at a different level of mastery – it would have been nice to have an undo button that momentarily pops up, so I could have a second to undo that mistake! Instead I just set everything back to 0% mastered, oh well, I’ll learn them all again.