Add dcat ap export plugin

[PaulBoon]

No description provided.

[akeldamas]

Hi @PaulBoon, a few questions:

1. I see two JARs are included: dcat-3-v0.8.4.jar and dcat-3-v0.8.5.jar. Since only v0.8.5 is used in install.sh, can the older one be removed from the repository?
2. As noted in your own comments, several config files contain hardcoded localhost URLs. Is it fine to leave these as-is for now, or is this something that still needs to be addressed?
3. I think the URL in dcat-dataset.properties line 32 uses & where it should be ?:

http://localhost:8080/datasets.xhtml&persistentId=${value}
# Should instead be:
http://localhost:8080/datasets.xhtml?persistentId=${value}

[PaulBoon]

Ok, it is a draft, but I did forget to temple some (or all?) of those URLs that now have localhost or the production portal in it.
Indeed I need to remove that old jar, it is just that the newer one is locally build by me for testing the latest plugin functionality.