jwt_delegate startup

[axl-pis]

Adds the jwt_delegate extension to the configuration file and is disabled by default. This addition also includes the url of a server that will receive the delegation of the authentication procedure.
jwt_gelegate is blocking. That is, as long as the verification by the delegated server is not accomplished, the following extension is not executed.
When the request response is retrieved, the "onreadystatechange" callback is executed.
The cases covered by the callback are :

• code 200 : the user's node is retrieved, we try to create it locally or we update it. Then we execute the following extension.
• code >= 500 : it means url errors or server crashes.
• code 401 : the authentication of the user on the delegated server has failed.