New features: you can add several rigid bodies, several markers and create new rigid_bodies

[Juancams]

Hi!!

As the title says, I have added the following:

• Renamed link_name to rigid_link to add a rigid_body.
• If you add multiple rigid_links, multiple rigid_bodies are created in different links.
• You can add marker_link in your plugin to add a marker on that link.
• Added service to group several markers in a rigid_body. The centroid of the polygon they form will be taken and the orientation will be given by the link that is specified.

For the CI to work and the package to be used, you first need to accept this PR

In the future, I would like to add an rqt plugin that can add new rigid, markers, and group markers in rigis, as well as being able to do it from mocap4r2cli.