Request logger

The complete Request-logger, it logs every request and checks if the user is behind a proxy (X-Forwarded-For). 
The Logger saves following Vars:
- Cookies
- Useragent
- Remote IP Address
- Request URL
- Proxy
The script needs a new table called 'requests'.

The Administrator may enable or disable the Logger by adding an option into the config file ''adhocracy.enable_request_logging' that may be True or False.