Implement EIP-4803

[acolytec3]

This was raised as a note in the most recent ACDE-E call that all clients should implement EIP-4803 which limits a transaction's gas limit to 2^63-1. We haven't actually implemented this yet so should go ahead and add it to our transaction classes. It's purely theoretical since this gas limit exceeds the max gas per block anyway but we should still do it to be spec compliant. I'm sure some EEST test will come along and find us out otherwise.