Navigating Directly to a Step

[mhspradlin]

When a user attempts to navigate directly to a step past the last step that was created, they should be redirected to the step past the last one they've completed or the first step.

A strategy that I think would work pretty well is to track the completed steps in FormStepper by adding another line to the onComplete/onBack it passes to each step that would set/unset a completed flag in a bit of state FormStepper tracks.