Unset http headers if necessary

This PR:
* should resolve https://github.com/sitn/crdppf/issues/175
* gets rid of the proxy stuff as we know that we can disable that through the telecom conf by the IT dept.

@asaunier, could try out this branch and tell me if it resolves issue https://github.com/sitn/crdppf/issues/175 ?
The proxy stuff should not be of your concern (it an internal SITN thing...)