Undo/Redo—initial implementation

WYMeditor's undo is, in some cases, not accurate.
I'm nervous about pushing out code that doesn't have tests. It's risky, since the tests may never be added, and the code may even be broken in some way. We're scientists, which means the onus is on us to prove our work. Show that what we claim to be true actually is true.

As a code reviewer, all I see are the diffs for changes on a per-issue basis. If I don't maintain a standard of "proving your work" on a per-issue basis, I can't be certain of the state of the code at any point, since it's not clear to me what tests may be missing.

The way I solve this problem is to either add the tests, or remove the untested functionality, and add both the test and the functionality together, as a unit.