make new paginated WorkflowEngine.getWorkItemsFor API to be able to select the order by attribute and ascending / descending parameter

allow former ( NXP-2481 ) existing method to throw WMWorkflowException: ResultSlice<WMWorkItemInstance> getWorkItemsFor( List<WMParticipant> participants, String state, int firstResult, int maxResult) throws WMWorkflowException; => calling code should be updated to handle that exception in case the WF engine is unable to get the tasks. add new method to the WorkflowEngine interface: ResultSlice<WMWorkItemInstance> getWorkItemsFor( List<WMParticipant> participants, String state, int firstResult, int maxResults, String orderBy, boolean orderAscending) throws WMWorkflowException; Eventual implementing classes should be updated accordingly.