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.

[area]

Would it be possible to move the creation of ColonyRewards in to a new PR that could be reviewed (presumably quickly) separately? I find it very hard to keep track of what's changed when large chunks also move around.

[area]

There's a lot of low-hanging fruit, branch-coverage wise, on setExpenditureValues. Don't just rest on the laurels of my commit you've cherry picked ;). Same for the new moveFundsBetweenPots.

This PR more or less solves two-out-of-three issues that I brought up in #1031... should it solve the third as well (i.e. the claim delay stuff)? Or leave that for another PR?

Cancelling an expenditure currently has no influence on reputation, which it is spec'd as (having the option of) doing.