[beta] Fix ethsign

[tomusdrw]

Not labelling as A8-backport since the code is completely different.

[gavofyork]

this is a little problematic. it blindly copies geth, yet:

• the documentation on the ethereum and parity RPC wiki contains an example which states the original ordering;
• oo7-parity.js assumes the original ordering;
• at least one dapp the same.

[tomusdrw]

• Example here: https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign contains a RSV signature.
• Parity wiki is a bit outdated (was auto-updated, but some manual changes were lost it seems), doesn't even mention that the data is altered before signing: https://github.com/paritytech/parity/wiki/JSONRPC-eth-module#eth_sign
• It brings back the ordering we had since the very 1.0 version and is used by other providers as well (Metamask, TestRPC). I don't see a reason to keep it as VRS but see a point in having a cross-client compatible API.

[gavofyork]

ok the EF changed the wiki spec (unilaterally - how surprising) to fit the geth impl.

https://github.com/ethereum/wiki/wiki/JSON-RPC/_compare/c4321dedf743c6e0d9dd5d3679b028cae46eef7c...3dea1229fb5a23188798075d6127406a1ab70690

may as well play along.

[tomusdrw]

Seems that build failure is not related to my changes. @paritytech/ci could you guys have a look? kcov is not installed?