Add Email/Password authentication

[nlaz]

Description

Some hackathon projects will want to be able to use their own login system. Our example app should support users signing up and logging on using typical email/password credentials. This was not included originally with the starter kit because (IMHO) it adds unneeded complexity to applications to support custom logins. However, our starter kit should probably be more flexible.

[samflab]

I want to work on this issue