Integrate WebWork (User Creation, Login)

Currently supports:
1. Creation of WebWork user from grapefruit, automatically when the user first tries to view problem sets
2. Auto-login to WebWork interface in iframe

Important notes:
1. Requires configuration changes (/config/database.yml requires WebWork information)

Still coming:
1. Documentation about above configuration
3. Better navigation
2. WebWork grading results in grapefruit?