Update HypermediaAutoConfiguration to apply the Jackson2HalModule to
the primary ObjectMapper. This restores the behavior of Spring Boot
1.1 where HATEOAS types could be serialized for both `application/json`
and `application/json+hal` content types.

A `spring.hateoas.apply-to-primary-object-mapper` property has also been
provided to opt-out if necessary.

Fixes gh-2147