Add suport for loading SDF scenes generated by blender BIM to robotics addon

Requires:

• sw/armarx/meta/axii!517 (merged)

This merge request allows to load a scene described by an SDF file (generated by the BIM to robotics blender addon), instead of using a JSON. For this, the following requirements have to be met:

1. The SDF file must use includes for each model, and each model directory contains an URDF file.
2. The SDF include paths must not lead to a location that can be resolved by SDFormat by default.

The second condition is necessary because SDFormat 6.0 apparently does not allow getting the original include paths (https://github.com/gazebosim/sdformat/blob/sdf6/src/parser.cc#L916). Therefore, the fallback mechanism when a path is not found is used to retrieve all include paths. Using a newer version of SDFormat would probably solve this, but could require some Axii modules.

The code uses SDFormat 13, which is part of the following Axii merge request: sw/armarx/meta/axii!517 (merged) This allows accessing the original paths and setting search paths for URIs on a per-SDF-file basis.