InteractionManager: add getter in OSMD class (#15)

src/OpenSheetMusicDisplay/OpenSheetMusicDisplay.ts

@@ -1013,6 +1013,9 @@ export class OpenSheetMusicDisplay {
     public get EngravingRules(): EngravingRules { // custom getter, useful for engraving parameter setting in Demo
         return this.rules;
     }
+    public get InteractionManager(): AbstractDisplayInteractionManager {
+        return this.interactionManager;
+    }
     /** Returns the version of OSMD this object is built from (the version you are using). */
     public get Version(): string {
         return this.version;