Only poll for events from confirmed blocks

[hackaugusto]

Abstract

Reorgs may change the order transactions are executed, the new order may make a previously successful transaction fail, or change the order of events. To avoid races we need to wait for the blocks to be confirmed.

Motivation

This has introduce a few bugs #2449 #2658 #2664

Specification

The event filter should just lag behind by confirmations blocks.

Backwards Compatibility

This will not introduce backwards compatibility issues, but it will add a bit of latency for the secret registration, which is not a problem with the current version of the smart contracts because of the secret registry.

Related

Take chain reorg into account #1121

[palango]

Fixed by #2671