[Finishes #74059246] Finish step before allowing next step

Attempt to make maze animation/stepping code a little clearer while also making sure we disable the step button while we're animating a step.  I'm not entirely convinced I made the code clearer, so do let me know if/what is still confusing.

Important scenarios I've tested:
(1) Solution with infinite loop (we still animate correctly with stepSpeed 0).
(2) Standard solution success/failure
(3) Step mode success/failure and can't step before finishing last step.
It's just an array of steps.  This is for situations like K1 North (which is really a turn and a move).  I'll perhaps try and add a clarifying comment.