NFR: Add undo support

[aleemb]

Not sure if this is in the scope but would be nice if undo/redo support was added. I think this is achievable by pushing/popping the states in a stack.

[dcousens]

Could you elaborate on what you might expect this to do? And perhaps why it couldn't be done by the parent component?

[aleemb]

Please feel free to close this as this is not critically important but if you add two selections, ctrl+z could undo those selections. I believe react makes this fairly easy due to statefulness.

On a related note, I felt the need for this because I hit escape to dismiss the dropdown and then hitting it again deleted all my selections which I am sure will bite a lot of users. So maybe escape should not act as a delete all especially since the key is already overloaded to dismiss the dialog.

[TrevorBurnham]

This would be especially helpful after pressing backspace to remove an item in multi-select. It's an easy mistake to make, and you may not remember what you deleted.