* Dependency updates:
  * All dependencies are updated to their very latest versions.
  * PHPUnit:  A new class is used for TestCase, so each test is updated
  * Money/Money: A couple method name changes required small updates
  * Added PHP 7 constraint
  * Added roave/security-advisories for security checks
* Build update: Assumes composer is already installed on the host machine
* Add OrderLine::toArray() method for logging convenience
* Cleaned up unused `use` statements and redundant `implements` statements