some slug prefill logic (bug 1041722)

Once you start typing into the name field replace all spaces with '-'. Once you deselect you get no more prefill love which also takes care of other locales trying to override the existing slug. It's possible other logic could be added but I couldn't think of any for now.
What if instead of doing this, we change the value of the `placeholder` attribute on `input`, and on submit, if the field is empty, do `$slug.val($slug.attr('placeholder')`?

Then you won't need to awkwardly store state, you can let the browser manage the overriding, and there's a built-in visual cue that it's being autofilled.