ACT-1739: Added support to Message Boundary Events in Modeler
ACT-1739: Removing the namespace from the message id if set
Improving "cancelActivity" attribute handling with JsonConverterUtil.getPropertyValueAsBoolean(name, objectNode, defaultValue)
Merge pull request #235 from mikedias/boundarymessage

ACT-1739: Added support to Message Boundary Events in Modeler