Log signed messages in state logs on mobile

We should be storing a history of signatures, especially as we move to a more counterfactual/metaTx world, and more txs are replaced by signatures.

Especially in the wake of the OpenSea/Wyvern phishing campaign, having good forensics of past signatures would be extremely useful.

Acceptance criteria:
- Log all signed messages (signTypedData, signTypedData_v[x], personal_sign, eth_sign)
- Log the origin that proposed the messages
- Log when the message is signed
- Results should be available in state logs

Stretch goals
- Show these signatures in the [state-log-explorer](https://github.com/MetaMask/state-log-explorer)

Start by tracing the mobile entry points for signTypedData, signTypedData_v[x], personal_sign, and eth_sign, then follow how state logs are recorded. Done means every signed message includes its proposing origin and signing time in state logs; the state-log-explorer integration is a stretch goal.

Written by the indexing model from the issue text.