Add initial user functionality

This is a big PR that adds Devise and hooks up user sign-up/sign-in/sign-out and account management.

To get it up and running you'll need to:
* Run `bundle update`
* create a `.env` file with the following entries:
  * `PORT=3000`
  * `EMAIL_SENDER=[replace me]`
  * `MANDRILL_USERNAME=[replace me]`
  * `MANDRILL_APIKEY=[replace me]`

The format for `EMAIL_SENDER` would be `My name <myemail@example.com>`
You'll need to sign up for a [Mandrill](https://mandrillapp.com) account. The `MANDRILL_USERNAME` and `MANDRILL_APIKEY` can be found from SMTP & API settings from the settings dropdown menu (far right) when you've logged in.

* You now need to start the rails server with `foreman start`

Until you have the email setup with Mandrill correctly you won't be able to sign up as confirmation emails are required to, er, confirm your account and allow you to sign in.

Once you've got it up and running you'll notice that:
* All the expected user management is in place (sign up/out, account editing, forgot password links, re-send confirmation links etc. etc.)
* I've added twitter-bootstrap to style the pages a little better.
* You now have to sign in/up to start using the data-entry pages. 
* You can browse the existing data via the browse link on the home page without being signed in/up. (Of note AnnoJ doesn't appear to be working properly as it seems to be expecting a certain `id` in the database?)
* All the cucumber features are passing but they only cover a small part of the existing functionality so we'll need to continue to test the other sections of the site.

Any issues, let me know.