Set correct issuer on ERC725 claims

[tyleryasaka]

Each claim, at the contract level, has a field for issuer. This is not used for signature validation, but it does keep the claim id's unique. What we have works for Origin purposes, but to be fully ERC725 compliant we should be populating this field with the public key of whatever issuer was used to sign the attestation.

Really then, the server that is returning attestations should return the issuer as part of the response. Then we can simply pass that data through to the identity contracts.

This is not a high priority at the time of this writing.