OPENENGSB-3270 Sending of 'Object' instances with JSON, removes their subtype

* convert from Map to desired type (SQLCreate) directly instead of converting it to string and then parsing the string into a SQLCreate object.

see http://issues.openengsb.org/jira/browse/OPENENGSB-3270#comment-16823

Warning! Do not merge before merging loom-java first as it uses the newly introduced helper method.