Definition of properties under dcat:Resource use inconsistently "item" and "resource".

Some examples:

Definition of dcterms:creator in §6.4.4 Property: creator:

The entity responsible for producing the resource.

Definition of dcterms:description in §6.4.5 Property: description:

A free-text account of the item.

The same situation occurs also in other parts of the specification.

The proposal is to replace "item" with "resource" wherever it refers to an instance of dcat:Resource.

This proposal is implemented via PR #1491