switch to getTenderReferencedDocument analogue to getContractReferencedDocument, added DatedReference class and setters/getters for Invoice

library/src/main/java/org/mustangproject/DatedReference.java

@@ -0,0 +1,46 @@
+package org.mustangproject;
+
+import org.mustangproject.ZUGFeRD.IDatedReference;
+
+import java.beans.BeanProperty;
+import java.util.Date;
+
+public class DatedReference implements IDatedReference {
+
+	protected String ID;
+	protected Date opDate;
+
+	public DatedReference setDate(Date opDate) {
+		this.opDate = opDate;
+		return this;
+	}
+
+	public DatedReference setID(String ID) {
+		this.ID = ID;
+		return this;
+	}
+
+	public DatedReference() {
+
+	}
+
+	public DatedReference(String ID) {
+		setID(ID);
+	}
+
+	public DatedReference(String ID, Date theDate) {
+		setID(ID);
+		setDate(theDate);
+	}
+
+
+	@Override
+	public String getID() {
+		return ID;
+	}
+
+	@Override
+	public Date getDate() {
+		return opDate;
+	}
+}

library/src/main/java/org/mustangproject/Invoice.java

@@ -54,6 +54,7 @@ public class Invoice implements IExportableTransaction {
 	protected BigDecimal totalPrepaidAmount = null;
 	protected Date detailedDeliveryDateStart = null;
 	protected Date detailedDeliveryPeriodEnd = null;
+	protected IDatedReference tenderReference = null;
 
 	protected ArrayList<IZUGFeRDAllowanceCharge> Allowances = new ArrayList<>(),
 		Charges = new ArrayList<>(), LogisticsServiceCharges = new ArrayList<>();
@@ -144,6 +145,34 @@ public class Invoice implements IExportableTransaction {
 		return number;
 	}
 
+
+
+	@Override
+	/***
+	 * BT-17
+	 */
+	public IDatedReference getTenderReferencedDocument() {
+		return tenderReference;
+	}
+
+
+	/***
+	 * BT-17
+	 * @param dr
+	 * @return
+	 */
+	public Invoice setTenderReferencedDocument(DatedReference dr) {
+		tenderReference=dr;
+		return this;
+	}
+	
+	public Invoice setTenderReferencedDocument(String ID) {
+		DatedReference dr=new DatedReference(ID);
+		setTenderReferencedDocument(dr);
+		return this;
+	}
+
+
 	public Invoice setNumber(String number) {
 		this.number = number;
 		return this;

library/src/main/java/org/mustangproject/ZUGFeRD/IExportableTransaction.java

@@ -219,7 +219,7 @@ public interface IExportableTransaction {
 	 *
 	 * @return mandatory ID, optional Date
 	 */
-	default IDatedReference getTenderReference() {
+	default IDatedReference getTenderReferencedDocument() {
 		return null;
 	}