* Added basic Escrow

* PullPayment now uses an Escrow, removing all trust from the contract

* Abstracted the Escrow tests to a behaviour

* Added ConditionalEscrow

* Added RefundableEscrow.

* RefundableCrowdsale now uses a RefundEscrow, removed RefundVault.

* Renaming after code review.

* Added log test helper.

* Now allowing empty deposits and withdrawals.

* Style fixes.

* Minor review comments.

* Add Deposited and Withdrawn events, removed Refunded

* The base Escrow is now Ownable, users of it (owners) must provide methods to access it.