Add support for utheque when loading the URDF

[jbmouret]

• The support is optional
• No additional runtime dependency (since utheque is header only)
• This will search the URDF from the YAML file in the utheque paths

[dalinel]

Nice it works well like this

Maybe we should also do something for the base_path parameter in another PR

[dalinel]

I think it is ok to merge this PR now