Signaling the user that they have signed in or signed out

[hanseaston]

Right now, when the user either signs in or signs out, there is no obvious change in the interface to indicate their action has succeeded. We want to display a message (or a quick pop-up component to indicate that) instead. Definitely don't use alert(). I feel like that would ruin the user experience since that strategy doesn't align with the rest of the app.

Whoever is interested in tackling this might need to fire an action based on the Firebase's onChangeListener.