fix(exports): export Vexflow graphical classes (e.g. VexflowGraphicalNote)

part of #549

src/MusicalScore/Graphical/index.ts

@@ -49,3 +49,4 @@ export * from "./SystemLine";
 export * from "./SystemLinePosition";
 export * from "./SystemLinesEnum";
 export * from "./VerticalGraphicalStaffEntryContainer";
+export * from "./Vexflow";