Skip Invalid Deposits, Add Deposit Index Ordering - (Spec PR #589, #594)

[schroedingerscode]

Description

As an implementor, I want to add mandatory deposit index ordering so that block proposers may skip invalid blocks and Artemis is in sync with the Beacon Chain spec.

Acceptance Criteria

• Ensure process_deposit logic does not fail the entire block when an invalid proof of possession is provided. (See PR 589 below.)
• Add deposit_index to BeaconState.
• Initialize deposit_index in get_initial_beacon_state.
• Verify that deposit.index == state.deposit_index in processDeposits section of per-block processing.
• Increment state.deposit_index after processing the deposit in deposits section of the per-block processing.

Additional Information

• See Silently skip deposits with invalid proof in process_deposit ethereum/consensus-specs#589
• See Add mandatory deposit index ordering ethereum/consensus-specs#594

[vitorpy]

Working on this.

[schroedingerscode]

Closed by #454