Fixes for a number of things, including JAXB/marshalling problems, JSON marshalling and others

BZ 1001527: Added FindProcessInstanceCommand and other jbpm-audit commands to the right places (AcceptedCommands, JaxbSerializationProvider)
BZ 1002927: Adding JSON support
(cherry picked from commit d6815178305320eca2a1ea671ba36d54476bfbc3)