refactor: added a GraphicalVoiceEntry holding the GraphicalNotes of one voice. The inherited VexFlowVoiceEntry holds then also the corresponding VexFlow.StaveNote.

src/MusicalScore/Graphical/VexFlow/VexFlowVoiceEntry.ts

@@ -0,0 +1,11 @@
+import { VoiceEntry } from "../../VoiceData/VoiceEntry";
+import { GraphicalVoiceEntry } from "../GraphicalVoiceEntry";
+import { GraphicalStaffEntry } from "../GraphicalStaffEntry";
+
+export class VexFlowVoiceEntry extends GraphicalVoiceEntry {
+    constructor(parentVoiceEntry: VoiceEntry, parentStaffEntry: GraphicalStaffEntry) {
+        super(parentVoiceEntry, parentStaffEntry);
+    }
+
+    public vfStaveNote: Vex.Flow.StaveNote;
+}