Adds a really basic nat manager that attempts to use UPnP to punch
a hole through your router for any IPV4 tcp addresses you have
configured.

Adds any configured addresses to the node's observed addresses list
and adds observed addresses to `libp2p.multiaddrs` so we exchange
them with peers when performing `identify` and people can dial you.

Adds configuration options under `config.nat`

Hole punching is async to not affect start up time.

• Commit d240b9c
• Compare 4abea7f..d240b9c
• Branch feat/add-upnp-nat-manager

Alex Potsides