Traffic encryption option

[nicorusti]

In one of the latest TC standardisation, @rlapuh suggested to support optional traffic encryption. This would represent a long-term evolution. I leave this idea here open for further discussion.

I do think SCION should consider including a traffic encryption option into its solution with integrated key management. I believe security is the key angle of SCION to penetrate the market. Relying on external encryption and key management and not having an integrated option is sub optimal in my mind.