Implement support for CLARIAH Tool Discovery output (LOD -> CMDI conversion)

[proycon]

In CLARIAH/clariah-plus#37 (comment) we determined that the
best way to achieve interoperability between CLARIAH's tool discovery pipeline and CLARIN's VLO is by exporting our codemeta/schema metadata
to CMDI; the creation of such a CMDI profile is tracked in CLARIAH/tool-discovery#31.

We determined that most logical place to do such a conversion is in the CLARIN
OAI Harvest Manager (which @menzowindhouwer & team already expanded to handle
linked data (dcat) for CLARIAH's FAIR Data track), this currently lives in a
fork at https://github.com/CLARIAH/oai-harvest-manager and needs to be merged
back here at some point. (the fork itself has no issue tracker so I open this here upstream)

This issue aims to track the progress on adapting the harvester to handle the
CLARIAH tool discovery output. I'm not really informed on what exact changes are
needed in the implementation, but @menzowindhouwer can probably fill the gaps.