#7 - Ensure only valid Addresses can be stored

In this issue we will implement the second test case, which is dealing with the Address entity.

• test validation of Address entity
• create ValidationVerification Test API abstraction, to more easily test for validation violations
• split test cases to check one aspect on every test
• refactor CustomerIntegrationTest to use the new ValidationVerification Test API
• make ValidationVerification more generic through Java generics