Simpler Way to Navigate Through Tests

[brodieG]

Right now we use ENTER at an empty prompt to re-prompt, which is a pretty wasteful use of the simplest key stroke. Particularly in review mode, it would be nice if we could just hit ENTER to advance through tests. ENTER at an empty prompt should basically be a 'no-change-to-unitizer' command. So we don't add new tests, we don't remove passed tests, etc.

Implementing this will be more obvious once we implement #193.