Add user registration.

### What is the problem / feature ?

The Volunteer Database was in need of user registration

### How did it get fixed / implemented ?

Added the following user registration flow.
- A user initiates registration with an email address
  - If the email address is already taken, an error is shown to the user.
  - If there is no user registered under that email, a tokenized link is sent to that email address.
- The tokenized link expires in 48 hours (we can change this)
- Following the tokenized link takes you to a page with a `password` and `confirm password` form, that when submitted, creates a user with the give email address and logs them in.

### How can someone test / see it ?

Follow the registration process.

@Zaskoda, I didn't do much to make these pages pretty.

*Here is a cute baby animal picture for your troubles...*

![catmousebunnydog](https://f.cloud.github.com/assets/824194/2369208/01f48f78-a7d4-11e3-903c-4f1458f60b58.jpg)