add user audit

Logs would look like this before and after login:

```
--------------------------------------------------------------------------------
DEBUG in server [/service-frontend/service/server.py:16]:
Audit: user=[anon], request=[<Request 'http://localhost:8000/login' [POST]>]
--------------------------------------------------------------------------------
127.0.0.1 - - [29/Jul/2014 22:36:26] "POST /login HTTP/1.1" 302 -
--------------------------------------------------------------------------------
DEBUG in server [/service-frontend/service/server.py:14]:
Audit: user=[1], request=[<Request 'http://localhost:8000/' [GET]>]
--------------------------------------------------------------------------------
127.0.0.1 - - [29/Jul/2014 22:36:26] "GET / HTTP/1.1" 200 -

```

Note how ```user``` goes from ```anon``` to ID ```1```.