Document objectMapper configuration

[tobilarscheid]

Explain that JsonInclude.Non_Null is only needed until the next release of swagger-jaxrs
Once it is out, we can completly remove the line

[tobilarscheid]

As this functionality is finally merged in the swagger-jaxrs code, can we merge this example please?

[martinraie]

I assume this commit is not necessary anymore as swagger-api/swagger-core#2106 has been reverted in swagger-api/swagger-core#2349?

This row should still be removed:
environment.getObjectMapper().setSerializationInclusion(JsonInclude.Include.NON_NULL);
but replaced with this:
environment.jersey().register(SwaggerSerializers.class);