Adding decay time to PointCloud2

[Pandananana]

It would be very valuable for me if it was possible to have the PointCloud2 stay visible for a set amount of seconds, so that I can easily see what I have scanned already, and to see if overlap is too much or too little.

This PR is relevant, but is flawed: #357

If there is an easier / better way that doesn't require modifying ROS3Djs I would also like to know.

[MatthijsBurgh]

I don't have the time to implement this. In case you write the code, I am happy to review it.

[Pandananana]

Ok I will look into it. I am guessing it should include a unit test, as mentioned in the other PR?

[MatthijsBurgh]

That is indeed very desired to keep it maintainable in the future.