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
BZ1014071 - DataModelOracle: Performance issues when model is large

(cherry picked from commit 711b69ef54807aaa1f867d3ab6bfe67baa02cd28)
JBPM-3814, BZ 1002724 Bugfixes with regards to concurrency