Add "view all nodes" to rqt_rosmon GUI

[zlacelle]

If we've got a bunch of rosmon launches with different launch files, it would be good to be able to view all running nodes and their corresponding CPU/Memory usage and state in one place. Can the rqt_rosmon gui be enhanced with a "view all" tab?

[xqms]

It certainly can be done. Here's what I would do:

• add a special [all] key to ROSMonModel
• add a slot to MonGUI that listens to ROSMonModel updates and creates subscribers for each rosmon topic
• extend NodeModel to save a "source topic" for each entry, and modify the NodeModel::updateState() method:
  • add a parameter "sourceTopic"
  • add logic that adds/removes nodes belonging to that sourceTopic.

I won't have time for this in the near future. But as always, PRs are welcome!

[zlacelle]

Makes sense. I can probably tackle this slowly over the next few months. Thanks!