This fixes the remaining undo/redo test.

Problem #1: It looks like we must use fake timers if we want the store state to be updated based on database operations (e.g., if we use initialize() to reload the state). I think this is because the thoughtspace operations are asynchronous and don't call the store operations prior to the test ending. (I'm not sure why we didn't get other errors that made this clear.)

Problem #2: There appears to be some store state that isn't cleaned up between tests that persists from the previous tests and breaks this one. The other tests probably aren't effected because they all call createTestStore, which presumably creates a brand new store.

This second issue is somewhat ancillary but might come up when mixing tests that do/don't require createTestStore and should figure out the root cause at some point. My initial guess is that we'll just need to figure out a way reverse whatever happens in createTestStore.

Closes #2145