Expenditures extension, utilities, updates

[kronosapiens]

Closes #1042

• Add StakedExpenditure for creating expenditures via stakes, and reclaiming or slashing stakes

Also:

• Add a new moveFundsBetweenPots which accept arrays of tokens & amounts
• Add a refundDomain private function which returns excess funding back to the domain on claiming of payment
• Add a setExpenditureValues function which can change all expenditure values in one transaction, for owners
• Add a setExpenditurePayout function to update slot payouts with correct bookkeeping, for arbitrators

The introduction of setExpenditurePayout addresses a bug in the existing implementation, where using setExpenditureState to update payouts would allow the funding pot bookkeeping to fall out of sync. setExpenditurePayout as an arbitration function provides an alternative for arbitrators (with an eye towards motions) to update payouts with correct bookkeeping. This introduction has necessitated an update to VotingReputation to correctly handle both types of expenditure state changes.

[kronosapiens]

Regarding the slashing rep, I'll add an option to do so to the slashStake function.

I also think a cancelExpenditureAndSlashStake function which uses arbitration to cancel the stake & punish the creator in one go could be useful from a motions perspective. Thoughts? I was thinking through the specific flow... do we expect the slashing to occur while the expenditure is in the locked state? I suppose once the stake is slashed, there's no reason to go ahead and cancel the expenditure itself... unless to reclaim funds? Should we make cancelling the expenditure a part of the slash flow? Or include a boolean to that effect? That might be the move IMO.

Regarding the claim delays, that would require a v3 of the voting contract (since we'll be moving to a new way of accounting for claim delays), which I'd like to put into a separate PR. It may even be worth going back and finishing off #915 which includes this change.

[arrenv]

@area @kronosapiens You are correct. The expected flow is that slashing should occur when the Expenditure is cancelled, at any time after it has been put into a locked state.

The penalty makes sense to be configurable by a Colony when installing the extension.