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.

scripts/compile.sh

@@ -1,42 +0,0 @@
-#!/usr/bin/env bash
-
-# Configure to exit script as soon as a command fails.
-set -o errexit
-
-SOLC_05_DIR=solc-0.5
-
-# Delete any previous build artifacts
-rm -rf build/
-
-# Create a subproject where 0.5.x compilation will take place
-mkdir -p "$SOLC_05_DIR"
-
-cd "$SOLC_05_DIR"
-echo '{ "private": true }' > package.json
-npm install --save-dev truffle@5.0.0
-
-rm -rf contracts
-ln --symbolic ../contracts contracts
-
-# Delete any previous build artifacts
-rm -rf build/
-
-# Compile
-echo "
-module.exports = {
-  compilers: {
-    solc: {
-      version: \"0.5.0\",
-    },
-  },
-};
-" > truffle-config.js
-
-npx truffle compile
-
-# Modify the paths in the artifacts to make it look as if they were built in the root
-sed --in-place --expression "s/\/$SOLC_05_DIR//g" build/contracts/*.json
-
-# Copy them back into the root
-cd ..
-cp --recursive "$SOLC_05_DIR"/build build