refs #6039, closes#6047, closes#6048
- delete old/unused fixtures file
- add failing tests for #6047 & #6048
- redirect to sign-in if we get a 401 when making an API request
- fix incorrect `this.notifications` call in tag controller
- raise `authorizationFailed` action in application route's `sessionInvalidated` hook so that it can be handled by leaf routes (fixes re-auth modal display)
- close "saving failed" alert when successfully re-authenticated
- adds a "window-proxy" util so that we can override `window.*` operations in tests
- fix `gh-selectize` attempting to register event handlers when the component has already been destroyed
