Restore ExpenditureCancelled event on CancelAndReclaim

[area]

#1166 stopped the ExpenditureCancelled event being emitted when CancelAndReclaimStake was called - this restores the ExpenditureCancelled event as it was, an introduced an ExpenditureStakerPunished event.

I've also taken the opportunity to add an agent to our events where I thought it was appropriate - in particular, this brings the ExpenditureCancelled event in line with the ExpenditureCancelled event on the core contracts.