Expose corenet API

[magik6k]

This is continuation of #2005 , still WIP.
What it allows is to communicate in real-time using ipfs identities and libp2p. Currently the implementation uses websockets to communicate with daemon, and it implements channels over them, so the listener can handle more than 1 client at a time. Usage is still much like it was in #2005, but quite a few internals changed. I managed to set-up TAP tunnel over IPFS between 2 hosts using little helper program, so I think I can say that it at least works.
What needs to be done:

• Get sign-off under @AtnNn commit from Expose corenet on the command line #2005
• Clean up commit mess
• Implement/fix to closing connections
• Implement/fix graceful shutdown
• Cleanup code in few places
• Write tests
• Write docs

I'm opening this now so that people can see the progress and comment on what is done.

[ghost]

I haven't looked at the rest yet, but for API communication, @Kubuxu's unix socket proposal is very relevant: ipfs/notes#129

[whyrusleeping]

Yeah, this change is going to be (at least) two parts, the first being making the API transport more flexible, and the second is the actual exposing of the corenet stuff. lets start working towards part 1, sound good @Kubuxu ?

[whyrusleeping]

@magik6k can this be closed in favor of #3128 ?

[magik6k]

Yep, the other one implements the same thing.