Dumps from ShEx files

[labra]

Wdsub now supports --schema file.shex to pass and process a ShEx schema file.

Example:

prefix :  <http://www.wikidata.org/entity/>

<cities> {
    :P31 [ :Q515 ]
}

One issue is that the namespace for properties and entities is the same and is taken from the concept IRI, which differs from entity schemas which are based on RDF serialization.