leiten

* Make guest login working with new UserService
* Reuse existing guest username
* Adapted tests

This method uses transaction level READ_COMMITTED.

switch to oauth2 authentication which allows facebook, twitter, google
etc authentication

add spring-test and junit
add jetty plugin which allows mvn jetty:run

redirection

include config.properties.example and let override values by
config.properties
cas spring security configuration adjustments 

A session will be returned if one of the following cases are true:
* the session is active
* the session is inactive AND current (logged in) user is the creator

This should send a generated random username to the client that is valid
for the current HTTP-Session.

* Added session controller with method to get session by id
* Created session class to be used as entity object
* Created session service class and interface
* Added content negotiation view resolver to map entity objects to JSON

add servlet-api as provided dependency