Kill zombie windows

As described in #52, we have a zombie window problem:

1. Open a survey from a notification
2. Close the survey without submitting a form
3. Open another survey from the notification
4. The old survey that you closed will re-open (!!!)

This adds a hack to re-close all of the zombies as soon as they reopen.
If you kill the previously open tab, technically there should only be one previously open tab at any given time :)