create a "bitswap" contract

[jellegerbrandy]

This issue for now is more of a place holder than an actionable item, as the specifications are not at all clear yet.

The use case is: the IPFS nodes (or the ipfs signalling server) with yahya's mods keps track of bits sent and received, for each account. These transactions will need to be fomalized - probably via some form of state channels, and eventually on the blockchain.