Implement login screen designs

This PR addresses #63 and #118 by implementing the features:

- log in with google
- log in with email
- switch back and forth
- remember me
- tell user why they're here
- include a basic page that tells the user to check their email (looks nicer, but waiting on design)
- includes tests for the new functions

Includes a new `.login` wrapper class for login styling in the CSS.  Includes updates to warden to pass the `client_id` through to the login/session controller.

Here's an image of the output:

![myusa2](https://cloud.githubusercontent.com/assets/2539570/4048957/89b9cf8c-2d48-11e4-85c7-0ce464e6455a.png)