Add OAuth Security Service

The security module uses a combination of Agorava and PicketLink.
Agovara is used to handle the Twitter OAuth and is registered as a
PicketLink Autenticator.

'User' view is Identity.login().

AuthServlet is used to trigger the actual Login.

* Login via Twitter
* Create new user

Issue: #50
Add UI elements for Login/Logged in User

Uses the 'whoami' Security REST service to check if
current request is authorized or not.

Issue: #50