Use ZUGFeRD2PullProvider#buildNotes in inherited classes

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

@@ -22,6 +22,7 @@ package org.mustangproject;
 
 import java.math.BigDecimal;
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Date;
 import java.util.List;
 
@@ -679,6 +680,17 @@ public class Invoice implements IExportableTransaction {
 		return this;
 	}
   
+  public Invoice addNotes(Collection<IncludedNote> notes) {
+    if (notes == null) {
+      return this;
+    }
+    if (includedNotes == null) {
+      includedNotes = new ArrayList<>();
+    }
+    includedNotes.addAll(notes);
+    return this;
+  }
+  
   /**
    * adds a free text paragraph, which will become an includedNote element with explicit 
    * subjectCode {@link SubjectCode#AAI}