Feature/iotcore 110 restrict proxy function scope

Address the following issues:

https://github.com/telefonicaid/fiware-orion-pep/issues/7
https://github.com/telefonicaid/fiware-orion-pep/issues/6
https://github.com/telefonicaid/fiware-orion-pep/issues/3


Not sure what is X-Forawarder-For header and the processing that CB-PEP is doing with it, but if it is passed to Orion, note that Orion ignores it. Is that correct?

(In the X-Forwarder-For header explanation is complex, let's move to skype :)