Only disable notification checkbox if it's checked

We should always allow the user to manually opt-in to notifications on
action items.

Other JS fixes:
- notifications ajax request thing broke in this commit:
    9ca7808522b5ec1f778620168a467aecbd59d861
  and is fixed now

- The backbone apps are now loaded with main.js, since my JS
  re-organization broke that as well.
Merge pull request #137 from nikolas/allow-notification-opt-in

Only disable notification checkbox if it's checked