Adds traffic lights to the scene.

[francocipollone]

related to #834 related to https://github.com/ToyotaResearchInstitute/delphyne_demos/issues/38

Summary

• Obtains the traffic lights from the road network and creates models to be added to the scene.
• Creates a system for updating the traffic light models according to the current phase.

Notes on the implementation

The final output of the entire system is a ign::msgs::Scene message that is later on loaded by the Scene3D plugin(ign-gui3 builtin plugin) at delphyne_gui.

Sadly, once the scene is loaded, there is no way to edit the models, (the only thing you could do via a particular topic is to change the pose of the models). In our case, we wanted to change the color of the material of the traffic lights in order to simulate the different states in a semaphore. Other things that the Scene3d plugin allows is whether to remove the models or add new models.

So the workaround I ended up following was to delete the traffic light model when there is an update and add the model again. To do so visualizer/deletion and scene topics are being used. These two topics are later passed to the Scene3D plugin, in delphyne_gui when the visualizer is started.

• As result, it is visible certain flickering on the traffic lights due to that removing and adding process. I will fill a ticket with an alternative we could follow to avoid having this, but it isn't something trivial and it would require creating a new ign plugin in delphyne gui so as to interact with the scene(not via topics/Scene3d plugin interface).

Demo

4/1. New demo updated:

https://user-images.githubusercontent.com/53065142/161300594-2ee077b2-a4b5-45f8-ab16-47aee07418cb.mp4

Pendings

• [x] Improve/complete docstring documentation

[francocipollone]

1 - Docstrings for improving documentation was added. 2 - This PR doesn't add tests for the new systems that were created, however, the behavior was verified through the integration demo added at https://github.com/ToyotaResearchInstitute/delphyne_demos/pull/41. An issue will be created for adding tests later on as this PR has already several lines of code.

[liangfok]

Let's squash the three commits into one.

[francocipollone]

Let's squash the three commits into one.

Done!