Suggestion: logout to return a promise

Why not have FirebaseAuth.logout return a promise?

Version info

Angular: 2.0.1
Firebase: 3.4.0
AngularFire: 2.0.0-beta.5

Use case

Most of the time, if not always after logout you'll need to redirect.

Debug output

Here is what I mean: line 89
https://github.com/youpage/angular2-firebase/blob/master/src/auth/services/auth-service.ts

And the call from the Toolbar: line 26
https://github.com/youpage/angular2-firebase/blob/master/src/layout/components/toolbar.ts

Expected behavior

FirebaseAuth.logout should return a promise

Actual behavior

No returning behaviour

Thank's

P.S. Other than this, great job guys, I love it.