Redirect the user after submitting an update

The javascript Form object we were using for all forms had some logic in it for a specific form. So first, I'm splitting that specific behaviour so a CommentsForm sub-class, to keep the parent form object more generic.

Once that's done, we can add a new UpdatesForm sub-class, which just redirects after the new update was submitted.

Right now, it's redirecting to the list of updates submitted by this user. Maybe it would be better to redirect to the user profile? To the update display page?