Facebook single sign on

Velruse is used to authenticate the users.

Includes:

- configs, so the velruse service can be controlled with supervisor
- creating new users with the Facebook login
- connecting existing users with Facebook, allowing them to use the Facebook login, too
- a forward and backwards migration for the the table which holds velruse users
- unit tests on the model of velruse users
- integration with the openid login interface
- possibility to use velruse for other services (openid, twitter...)

In the course of integrating the Facebook login with the openid login, I intruded an openid html file. Its nothing bad, the inner workings of the openid login have not been touched.
I did this because tweaking the openid JavaScript plugin to work for me seemed as hard as replacing openid with velruse altogether.

Facebook single sign on is turned on by default.