Create Graph Using ROS Bags

[shouhengyi]

I'm wondering if it is possible to create a graph JSON file just using the ROS bag. Very often, people don't have access to the code base when debugging issues. For example, field engineers, triage engineers, etc.

If this is achievable, it opens up the opportunity to integrate LaunchMap with bagel. This will be very cool and helpful for developers doing offline analysis on their ROS bags.