Add importing from SHACL

[dalito]

We (@StroemPhi @markdoerr @HendrikBorgelt) were looking for DCAT-AP represented as LinkML model. For DCAT-AP SHCAL shapes are published which would be an ideal start. The conversion has once been done manually by Hendrik but we are interested in getting this done in an automated way.

Having an importer that could create LinkML models from SHACL would be ideal to accelerate the process and avoid errors.

I may start to work on this soonish in my fork.