Add initial support for SDF files

[zkingston]

No description provided.

[cohnt]

Looks like it has some issues with package paths. Not sure how easy it is to parse those, but it's not hard for a user to make all filepaths relative.

When I run it with relative paths only, it works*, but there seem to be some output issues:

1. The default filename is spherized.urdf (should be spherized.sdf).
2. The top level SDF tag has a path element, which shouldn't be present.
3. Relative filepaths will be broken (again not the end of the world -- can be switched back with package:// syntax)
4. Each <collision> tag needs a name, and names can't be repeated within a link.
   With these items fixed, I get the following working output:

I've also attached a zip file containing the original output and the fixed output.
sdfs.zip

[zkingston]

Thanks for checking it out! Addressed everything you said, pulled in this package to resolve paths.

[cohnt]

That's great! Thanks for putting this together so quickly.

Like I said, long-term, it would be great if packages could also be resolved. (I've usually seen this done by reading an environment variable like ROS_PACKAGE_PATH.) But with relative filepaths only, everything looks right!

[zkingston]

Oh, do the package URIs not work? There should resolution of the URIs now. If it doesn't work, no big deal, add that to the feature list to handle soon.

[cohnt]

Looks like paths aren't resolving correctly -- its currently concatenating the path to the sdf file and the path after the package:// bit. The command

resolve-robotics-uri-py --package_dirs $ROS_PACKAGE_PATH package://models/wsg_finray/meshes/one_piece_wide_grasp_finray_finger.obj

outputs

/home/tommy/Documents/programming/work/rlg/analytic-and-optimization-ik/codebase/models/wsg_finray/meshes/one_piece_wide_grasp_finray_finger.obj

which is correct. But when I call

python3 scripts/generate_sphere_sdf.py ~/Downloads/wsg50_110_finray_fingers_box_collision.sdf

I get the error message

FileNotFoundError: resolve-robotics-uri-py: No file corresponding to URI '/home/tommy/Downloads/combining_kinematics/models/wsg_finray/meshes/one_piece_wide_grasp_finray_finger.obj' found