xquery(bpmn-data): extracted database stuff in own class; implemented message creation handler
Merge branch 'bpmn_data' of https://github.com/BPMNData/camunda-bpm-platform into bpmn_data

Conflicts:
	engine/src/main/java/de/hpi/uni/potsdam/bpmn_to_sql/execution/CaseObjectUpdater.java
	engine/src/main/java/de/hpi/uni/potsdam/bpmn_to_sql/execution/DataInputChecker.java
	engine/src/main/java/de/hpi/uni/potsdam/bpmn_to_sql/xquery/XQueryHandler.java