IPFS DHT integration

[vyzo]

Wherein we take the firsts steps to integrate with IPFS:

• Refactors mcnode/proto to extract network related functionality
• Integrates libp2p-kad-dht and connects to the DHT as a client, with bootstrap through the IPFS planets; leeching ok for now per jbenet.
• Node.doLookup is modified to use the DHT for looking up peers as a fallback to directory lookup (or when there is no directory), and also caches lookup results with the standard peerstore ttl
• Fixes peer api operations to fail consistently with 404 when there is a peer lookup failure.
• Adds a /net/lookup/{peerId} endpoint to perform network lookups for debugging purposes

Closes #81

Example of node discovery through DHT:

$ mcclient listPeers
QmeiY2eHMwK92Zt6X4kUUC3MsjMmVb2VnGZ17DhnhRPCEQ
QmSp4R1R3rk7ho8M6P24sQG2yFiz8THYjwei468sz3GbSM
QmTVsocFCSEdPyM8dZ734GRhjvvmYyL9fShyezVkbPj17E
QmZ6dckUhRouVr6AsBTpK6vMLVpcz1KAeJAJVQEZQ5gCek

# DHT lookup!
$ curl http://localhost:9002/net/lookup/QmSbgwkKxtrBFDoGGwoKqH7soYiL64xpMK5oEYdiRnQGJp
/ip4/10.10.1.191/tcp/9001
/ip4/54.242.130.109/tcp/9001

$ mcclient id QmSbgwkKxtrBFDoGGwoKqH7soYiL64xpMK5oEYdiRnQGJp
Peer ID: QmSbgwkKxtrBFDoGGwoKqH7soYiL64xpMK5oEYdiRnQGJp
Publisher ID: 4XTTMGkYEx5trQX5VV32S82gguRMtVFQL5UDnZNHzyNEHKBeZ
Info: Mediachain Labs test node

[parkan]

The diff for net.go was being suppressed and I was very confused, makes sense now.