WIP: [#70] Convert to junit5

[mattrpav]

• [x] openwire-core converted and all tests passing
• [x] openwire-generator converted and all tests passing
• [ ] openwire-interop converted and all tests passing

Reviewer notes:

• [ ] junit5 does not support parameterized tests at class or beforeEach level
• [ ] junit5 asserts move the 'message' argument to the end... pay close attention to ensure test asserts are correct when reviewing
• [ ] DataStructureTestSupport renamed the class defined method assertEquals(object, object) to assertEqualsOpenwire(..) b/c it is re-entrant and causes confusion with the method-local fully qualified junit5 assertEquals(obj, obj)
• [ ] Note: Test coverage of openwire-core (by itself) is very low