IP resolution via stun server

As decided in menshen#39

Development plan

• have a module in menshen to retrieve public IP: deploy own STUN service to avoid hitting 3rd party apis.
• offer to optionally use 3rd party APIs (https / STUN)
• have an endpoint in menshen to lookup CC + ASN from a given IP (this can be used from inside a tunnel)
• send IP to menshen, get CC and ASN back (use it for reports, and for gateway selection in the case of riseup)

UPDATE: In this issue we focus on getting the current ip address via STUN (so a VPN is running and we can't just use a web api over https). In #15 (closed) we focus on the mapping ip address <=> country code