[UX] Hide/Show row weights should not be done globally without warning

When a user disables tabledrag, a cookie is set, disabling tabledrag on every page on the site. For someone who was just playing with that link to see what it did (most common use case) this creates a less-than-ideal experience and bad impression of the software.

What we really need instead of a cookie is a setting. People who want tabledrag disabled permanently should use the setting. People who need to disable it temporarily will use the link.