Add support for user sessions
Add a basic framework to handle user authentication
Implement CSRF
Rework the session handling to use a dispatch_view decorator
Store our sessions inside of redis

* Use msgpack to serialize the sessions for more compact
  storage and for faster serialization/deserialization
* Move the session cycling support into our RedisSessionStore
* Expire our redis sessions after 12 hours, but renew the session
  on every interaction with Warehouse
Use warehouse.utils.random_token for our CSRF tokens
Support ?next= urls on login to control the redirection
Add a page that allows users to log out of their session
Log when an error occurs trying to verify the user's password
Enable translations of the login form