DATAREST-238 - Changed JSON deserializer to ignore links.

Links are a read-only and basically have to be ignored during any inputs. This required removing the deserializer from PersistentEntityJackson2Module. This will cause the object mapping to fail as it doesn't know about the links property in the request body. Instead of requiring that every entity apply the necessary annotation, the mapper is configured to not fail on non-existent attributes. This allowed all the tests to pass while properly handling PUT operations.

Original pull request: #130.