Plugin Not Showing Any Admin Panel Menu or Page?

The plugin doesn’t do anything yet. I’ve been using Devlounges very old tutorial on creating a plugin using a class but it doesn’t seem to be working and I don’t know if it’s a WP version issue or something else. This is probably one of the best tutorials I’ve seen for creating a plugin using a class or period (well commented and makes sense as you read through the code) but I don’t know where the issue has arisen since I’m new to plugins. Can anyone help? I’ve included the code below. Thanks

[Code moderated as per the Forum Rules. Please use the pastebin]