Hello!
I have been working in a hosting company for almost 2 years and I have already created many addons. I made a package for fast admin pages developing and now I would like to share it with people.
The "WHMCS Easy Addons" will help you to create tabs for your addons and lists for your tables in a database.
Here you can take it: github.com/akerbel/whmcs-easy-addons
It has a readme file which helps you add the package in your addons.
If you would like to see a living example, you can look at my addon "Extended Logs". It adds two new pages for modules logs and activity logs, but with filters.
You can download it here: github.com/akerbel/whmcs-extended-logs
It also has a readme file with instructions.
PS The Easy Addons still supports WHMCS 5.