Switch usage of `vann:usageNote` for `skos:scopeNote`

[jakubklimek]

The range of vann:usageNote is rdfs:Resource (is a subproperty of rdfs:seeAlso). Currently in DSV, it is being used with literal values, which is incorrect.

Since usage notes are part of profile reuse, we will probably have to rework the DSV property value reuse, or change vann:usageNote to something else.

[jakubklimek]

skos:scopeNote is a good candidate, see SKOS and SEMIC Style Guide