Make Cook This! store the values in local storage to avoid loss on accidental nav

[barneyb]

After Cook This! starts, but before the recipe is imported, it should store the unsaved state in local storage (keyed to the URL), and then remove it upon import. That way if you navigate away, come back, and click Cook This! again, it won't reparse the document, but rather load from local storage (including any manual edits you performed). Explicitly closing the overlay should also clear, to allow an explicit re-import. Probably same goes for if it's clicked while it's already open (which is the current behavior).