Support sh:class constraints for SHACL validation.

[kburger]

Is your feature request related to a problem? Please describe.
When importing DCAT-AP 3.0.0 shapes and attempting to create a new metadata instance, sh:class constraints are always failing. The sh:class range for some properties is dcat:Resource, but entering valid dcat:Resource instance URLs will not pass validation.

Describe the solution you'd like
The validation should probably be performed with the proposed new instance projected on the entire FAIR Data Point graph. This way sh:class constraints are resolved against the existing instances in the graph.

Describe alternatives you've considered
An alternative is to manually relax or disable constraints in the imported shapes.

Additional context
See https://github.com/SEMICeu/DCAT-AP/blob/master/releases/3.0.0/shacl/dcat-ap-SHACL.ttl for the DCAT-AP shapes.