Decode raw solidity test event logs

[cgewecke]

Addresses truffle 745, where a third-party assertions library modeled on Assert.sol has been written and is being used exclusive of Assert.sol. There's no convenient way to link it to the test contracts and expose its TestEvent on their ABI. As a result, only the transaction receipt's raw logs are available and test failures aren't being processed correctly.

This PR adds a manual decoding step to the test evaluation step when a) the result.logs are empty and b) result.receipt.logs are not empty. It assumes the third party library will use a TestEvent function signature identical to the one in Assert.sol.

Needs tests but those will be over in the truffle repo.

[gnidan]

Looks good!

N.B. that SolidityCoder appears to be going away with web3.js 1.0, but this is already used elsewhere, so this PR doesn't introduce any additional problems.