RViz plugin - Building a display panel from .ui file

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So, I was able to create a simple display plugin. I was also able to create a panel plugin from a .ui file (similar to how it is done here).

Now I wanted to create a display plugin from the .ui file, so that instead of going to 'Add Panel' you'd just have to go to 'Add' and add your plugin like you would with any other display (similar to what it is done with MotionPlanning from moveit). I have tried several ways to do that but nothing seems to work. How would I do that?