Changed "overlay.key_provider.renew_interval" parameter to be in
seconds.
Minor changes.
Created possible DHTService interface.
Added DHTNode interface (it is supposed ti be inhrited by
OverlayConnection).
Added new class: KBucket.
It is basically an implementation of Bittorrent-like Kademlia K-buckets.

See more about K-buckets:

JS implementation of K-buckets:
https://github.com/tristanls/k-bucket
BitTorrent BEP-5:
http://www.bittorrent.org/beps/bep_0005.html