Allow login with e-mail address

[3rd-Eden]

I've seen a lot of failed requests in our logs where users are trying to login with their e-mail account instead of using their username. It could be that they have forgotten their username or that they are just accustomed to logging in using an e-mail address as that's something that a lot of sites allow.

To decrease these login failures we should just support e-mail based logging in. There are 2 easy approaches in to fixing this:

1. Use a regexp to check if the supplied username is a valid e-mail address and fetch the user resource based on e-mail adress.
2. Just fallback to checking the e-mail address if account isn't found.