DATAREST-397: Verify Spring Data REST integrates properly with Spring Security

Spring Data REST should be easy to apply method-level security controls. This issue contains a battery of tests verifying that method level security works as expected.

> **NOTE:** The only Spring Security dependencies added in this commit are test-scoped, meaning they don't add any extra depdencies to users of Spring Data REST.

This is also demonstrated by some canonical samples found in https://github.com/spring-projects/spring-data-examples/issues/21