Update Signer for Kusama upgrade

[jacogr]

For the Kusama upgrade, the signature is now a MultiSignature indicating the actual signature type as an enum. (Additionally the extrinsic format is now v4, just based on the extra indicator byte in the signature)

[pmespresso]

So we'll need the ECDSA function in Rust as well now then, @maciejhirsz? already there from Ethereum

[pmespresso]

I'd still leave this open, we're supporting sr25519 by default, but to fully support the MultiSignature we'll need to add support for ed25519 and ecdsa as well.

[hanwencheng]

Closed as duplicated with #614 .