Feature: Make use of Matched Events

[jaagut]

A new feature in iron called Matched events has been introduced. It makes it possible to get a callback if, e.g., a visualization tool subscribed to a topic, and thus dynamically turn on or off the generation of visualization topics.

https://github.com/fujitatomoya/presentation/blob/master/ROS_Iron_Irwini_Release/ROS_Iron_Irwini.md#matched-events

[ijnek]

That's an interesting new feature, how do you think RQt Image Overlay can take advantage of this feature?

Is the idea to notify the nodes that are publishing messages to rqt_image_overlay, about a user disabling visualization of a layer by unchecking the checkbox?