Navigator now supports converting controls to script-only stack behaviors

[Geoff Canyon]

I found one bug: if you try to save the script-only stacks in the same
folder as any of the stacks containing the objects you're converting, the
conversion process will hang partway through. The hang should occur before
anything has been changed, but still: Don't Do This.

I have a fix coded, but I'm in the middle of another update, so I will
update the whole thing tomorrow morning. (This is the sort of thing GitHub
is supposed to be good for, right? Heh -- need to figure that out...)