major: #200 Shared nothing architecture - last step to realise partition events

[astubbs]

Check:

• [ ] BrokerPoller can't access state - when performing commit, must request or be sent commit offset data by state owner (#419 )

Implements:

• #200
• Removes onPartitionsLost handlers as we don't need to do anything differently than from onPartitionsRevoked

Related:

• #271

Blocked by:

• #325

Causes:

• #419