CLPR: Payment Accounts and Key Integrations (POC)

This issues is can be closed after all entities that needs to sign off on state proofs are doing so, signatures are being validated, paired payment accounts are registered with each ledger, and the desired payment mechanics are in play for handling messages.

Chunks of Work

- [ ] Remote endpoints are signing state proofs with the node's signing key (requires having key in config)
- [ ] Local endpoints are signing HAPI state proofs they submit to the network.
- [ ] Synchronized payment accounts are registered with each ledger (HAPI Transactions)
- [ ] Messages are handled and are paid for by the indicated payment accounts.
- [ ] End to End tests needs to be created for scenarios where the payment accounts run out of funds to bill.

This issue needs to be broken up into sub-issues.