Suggestions for strings that select code

[effigies]

Following nipy/nipype#3183, we might want to think about how to make things more friendly for new users (or experienced users who've stared at code too long).

I think now we're having people import submitters directly, rather than accessing them via string arguments to workflow.run(plugin="..."), but when we do have those types of parameters, doing fuzzy-matching and suggesting a close option would be much more useful. If the list is small enough, listing all valid options would also be fine.