Various DCAT implementation fixes

Uncontroversial:

* The examples used `dcat:download` (which doesn't exist) instead of `dcat:accessURL` as documented by your schema. Fixed.
* DCAT uses the `dct` prefix for the Dublic Core namespace, not `dcterms`. This project now uses only `dct` consistently instead of both haphazardly.
* `publisher` and `language` are in the `dct` namespace not the `dcat` namespace.
* Updated all links to DCAT in the metadata resources (anchors had changed).

Potentially controversial?

* `xsd:boolean` (used for data quality) is not a property, it is a datatype. I switched it to a property in the temporary `ex` namespace, `ex:dataQuality` to make it valid RDFa.
* `dataDictionary` and `dataQuality` don't exist in DCAT anymore. `webService` and `feed` never existed in DCAT (closest are the classes `WebService` and `Feed`). I moved them to a *temporary* `ex` namespace.
* `foaf:Person` is a class, and therefore cannot be used as a property. Switched to `dcat:contactPoint` which the DCAT editors are currently adding, to make it valid RDFa.