Improved histogram example with Swing GUI
- HistogramGuiExample: improved layout management.
- fixed error in the DemonstrationWorkflowEngine and DemonstrationWorkflowEngineTest classes: use WorkflowInput[12] instead of input[12].
- fixed error in pom.xml: use examples.ConcatenateExample as the main class for the jar instead of the v1.WorkflowRunner class.