Escrows (#1014)

* 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* Add Deposited and Withdrawn events, removed Refunded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.

test/payment/ConditionalEscrow.test.js

@@ -0,0 +1,41 @@
+import shouldBehaveLikeEscrow from './Escrow.behaviour';
+import EVMRevert from '../helpers/EVMRevert';
+
+const BigNumber = web3.BigNumber;
+
+require('chai')
+  .use(require('chai-bignumber')(BigNumber))
+  .should();
+
+const ConditionalEscrowMock = artifacts.require('ConditionalEscrowMock');
+
+contract('ConditionalEscrow', function (accounts) {
+  const owner = accounts[0];
+
+  beforeEach(async function () {
+    this.escrow = await ConditionalEscrowMock.new({ from: owner });
+  });
+
+  context('when withdrawal is allowed', function () {
+    beforeEach(async function () {
+      await Promise.all(accounts.map(payee => this.escrow.setAllowed(payee, true)));
+    });
+
+    shouldBehaveLikeEscrow(owner, accounts.slice(1));
+  });
+
+  context('when withdrawal is disallowed', function () {
+    const amount = web3.toWei(23.0, 'ether');
+    const payee = accounts[1];
+
+    beforeEach(async function () {
+      await this.escrow.setAllowed(payee, false);
+    });
+
+    it('reverts on withdrawals', async function () {
+      await this.escrow.deposit(payee, { from: owner, value: amount });
+
+      await this.escrow.withdraw(payee, { from: owner }).should.be.rejectedWith(EVMRevert);
+    });
+  });
+});