Correctly persist checklist settings.

Incidentally, fixes an acceptance test (which would have caught this
bug) not running. Its step regex was "They are correctly selected
after I reload the page$", which happens to be matched by "I reload
the page$", another step definition. Lettuce seems to arbitrarily pick
between definitions if they both match a step, so it's good to ensure
that each step isn't a sub-regexes of another.
Merge pull request #465 from edx/peter-fogg/fix-stud-485

Correctly persist checklist settings.