title: Devise with Confirmable - Redirect user to a custom page when users tries to sign in with an unconfirmed email
body: <p>With the Confirmable module enabled, Devise will not allow an unconfirmed user to sign in after a predefined period of time has elapsed. Instead the user is redirected back to the sign in page with the flash message "You have to confirm your account before continuing".</p>
  
  <p>This is an undesirable interaction model, as a flash notice does not provide adequate space to properly explain to the user why access has been denied, what "confirm your account" means, provide a link to resend the confirmation, and instructions on how to check your spam folder and so on.</p>
  
  <p>Is there a way I can change this behaviour to redirect to a specific URL instead?</p>