dex/networks/eth: ETH fidelity bonds contract

[martonp]

This diff introduces the solidity contract that supports posting fidelity bonds on ETH.

ETHBond is a contract that allows users to post fidelity bonds. In order to
save on gas costs, the actual bonds are not stored in the contract, but rather
a commitment to the bond is stored, which is a hash of the user's address and
the current bonds they have posted. The actual values of the bonds should be
stored off chain, but they can be retrieved by checking the event logs of the
contract. The first bond for an account must be posted by calling createBond.
Any further updates to the bonds for an account, including adding, extending,
and refunding bonds should be done by calling updateBonds.

    === Gas usage ===

    Create 1: 72076 (first creation is higher due to creating the commitment array)
    Create 2: 54976
    Create 3: 54976
   
    Update:

     # Old
# New      0      1     2      3      4      5      6 
      1  41143, 42793, 50628, 55233, 59839, 64444, 69050
      2  45002, 57281, 52524, 60360, 64965, 69571, 74177
      3  48850, 61829, 67001, 62245, 70080, 74686, 79292
      4  52697, 66376, 71549, 76722, 71965, 79802, 84408
      5  56545, 70924, 76097, 81270, 86443, 81687, 89524
      6  60392, 75472, 80645, 85818, 90992, 96165, 91410

[JoeGruffins]

These tests are really cool. We need them for the current contracts.

[JoeGruffins]

I'm still reading up on how emit works, but is it ok at the beginning? Does it never happen if the tx fails?

[martonp]

Yeah, no log if the tx fails.

[JoeGruffins]

Can we get all of the values and locktimes upon restoration from seed?

[martonp]

Yes, you just check the latest log for the account ID. Actually the log should be updated to include the msg.sender.

[JoeGruffins]

Awesome! We can't do that with the utxo bonds yet.