Manually load the Nashorn Javascript Engine

The Nashorn Javascript Engine was deprecated in Java 11 and is no longer in the list of JavaScript engines that are automatically loaded by default. Resulting into the `javascriptEngine` being null when running the appframework module on Java 11

The Nashorn engine will eventually be removed in later versions of Java and hence we are advised to switch to `GraalVM`. But that is beyond the scope of this ticket.