Improve performance of undo of actions

[cmalinmayor]

Could save computed features, so they don't need to be recomputed. But, it requires more coupling of Annotators and basic Actions, which is complexity for not too much reward (in the unoptimized case, undo is the same speed as doing it fresh, which we think is mostly fine, more important to make the originals faster).

One proposed design is that Actions query the AnnotatorRegistry for the "old" values to save. Then the Actions can check for saved "old" values before recomputing them.