[FEATURE REQUEST] DynDNS support

[kirillkovalenko]

For those of us running instance from home it would be nice to have DynDNS support. it can be either build in feature via a public STUN server or push update feature via HTTP endpoint for ISP provided boxes such as FritzBox.

[SeverinAlexB]

#63 adds basic DynDNS support. This is a rough implementation which will be improved upon. See the following issues:

• [DynDNS] Improve IP change latency #65
• [DynDNS] Use Mainline to detect the external IP address #64

Let me know if you see other ways to improve upon it.