DATAREST-346 - Fixed invocation of overridden delete(…) methods.

We now defensively invoke the ConversionService prior to the reflective invocation of the delete method as we have to assume the clients providing the id value in a raw form, i.e. as obtained from the request and thus most likely as String.

Related ticket: DATAREST-335.
DATAREST-348 - Support for json-patch+json and merge-patch+json media types.

We now support PATCH request with application/json-patch+json [0] and application/merge-patch+json media types. The support is based on some customized usage of the FGE JSON Patch library [2]. 

As we need to apply the patch to an existing object, we need translate the JSON Patch remove operation into a replace operation setting the value to null so that out entity processing component registers the request for removal. Same applies to requests for merge-patch+json.

From an implementation point of view the handling of the media type has moved from the controller into PersistentEntityResourceHandlerMethodArgumentResolver and its delegates, n particular JsonPatchHandler. The application of the changes to the existing domain object is handled in the newly introduced DomainObjectReader.

Related ticket: DATAREST-345.

[0] http://tools.ietf.org/html/rfc6902
[1] http://tools.ietf.org/html/draft-ietf-appsawg-json-merge-patch
[2] https://github.com/fge/json-patch
DATAREST-337 - Fix trailing whitespace in poms.