Stake table: signature verification in the confirmation layer

[sveitser]

Currently we verify a BLS sig in the contract. We can do this in the GCL and avoid paying gas for it. We can also add a signature check with the for a signature with the schnorr key to ensure that the schnorr key is one the validator actually owns.

• [ ] Add signatures to contract events
• [ ] Update staking CLI to send schnorr signature to contract
• [ ] Check schnorr signature in GCL
• [ ] Check BLS signature in GCL
• [ ] Maintain backwards compatibility for existing stake table on decaf