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-337 - Fix trailing whitespace in poms.