Create a new social provider using Firebase email authentication

[dborkan]

Firebase has APIs to authenticate user's based on their email address: https://www.firebase.com/docs/web/guide/login/password.html - we should create a new FirebaseSocialProvider using email authentication.

For adding friends to the user's buddylist, we are thinking of extending the freedom social interface to include a new method like .addUser(userId), where for this email social provider userId could be the email address of your friend. Then if 2 users mutually add each other's userIds, they will appear on each other's rosters.