Migration to truffle 5 (and web3 1.0 (and BN)) (#1601)

* Now compiling using truffle 5.

* Migrated some test files, missing BN scientific notation usage.

* Now using BN time values.

* Migrate ERC20 tests.

* Migrate all ERC20 tests.

* Migrate utils, payment and ownership tests.

* All tests save ERC721 migrated.

* Migrated ERC721 tests.

* Fix lint errors.

* Delete old test helpers.

* Fix remaining crowdsale tests.

* Fix signature bouncer tests.

* Update how constants is used.

* Compile script pre-removes the build dir.

* Fix SafeMath tests.

* Revert "Compile script pre-removes the build dir."

This reverts commit 247e745113.

* Fix linter errors.

* Upgrade openzeppelin-test-helpers dependency.

* Update openzeppelin-test-helpers dependency.

* Define math constants globally.

* Remove unnecessary ether unit.

* Roll back reduced ether amounts in tests.

* Remove unnecessary toNumber conversions.

* Delete compile script.

* Fixed failing test.

test/helpers/constants.js

@@ -1,8 +0,0 @@
-const BigNumber = web3.BigNumber;
-
-module.exports = {
-  ZERO_ADDRESS: '0x0000000000000000000000000000000000000000',
-  MAX_UINT256: new BigNumber(2).pow(256).minus(1),
-  MAX_INT256: new BigNumber(2).pow(255).minus(1),
-  MIN_INT256: new BigNumber(2).pow(255).times(-1),
-};