drop emails and passwords into datomic, retrieve later

This merge lets a user sign up with an email and password. Much refactoring is needed, but it works for now.

@matthewward @bvanderveen please review, @matthewward I'd like to pair with you on some of the refactoring I want to do. I'm sure you'll have some great suggestions on how to make this work better and be less generally shitty.