fixes neeed in mldcat-ap-SHACL.ttl

[VladimirAlexiev]

https://semiceu.github.io/MLDCAT-AP/releases/1.0.0/shacl/mldcat-ap-SHACL.ttl:

• define and use this:

@prefix mldcatsh:     <https://semiceu.github.io//shacl/mldcat-ap-SHACL_en#>.

• The first line tries to define a list (collection) of all NodeShapes.
  However, the property doesn't exist, and even its URL is not ok (double //).

<https://semiceu.github.io//shacl/mldcat-ap-SHACL_en> <https://semiceu.github.io//shacl/mldcat-ap-SHACL_enshapes>

I don't know of any standard way to define a collection of shapes. However, you can:

• put them all in a separate graph (the "shape graph")
• use rdfs:isDefinedBy, eg

mldcatsh:AgentShape a shacl:NodeShape;
  rdfs:isDefinedBy mldcatsh: .