ISSUE-133 syntax simplifications & regularizations

After a quick offline discussion with Holger we would like to propose some
work towards syntax simplification

The proposal has 2 aspects that go together
1. we remove the sh:defaultValueType from SHACL (Peter also had concerns
with this - see issue-128)
2. we simplify sh:constraint in the following ways

a. sh:constraint is renamed to sh:node (other names welcome) and may have
only values of sh:NodeConstraint type
b. native sparql constraints (which could be used inside sh:constraint) are
now declared separately using a new property sh:sparqlConstraint that
allows only sh:SparqlConstraints

We believe this is a simplification everyone will like and would like to
put it in the agenda for the next telco. Any comments are welcome

rational for this change is the discussion for wording section 2.3.
sh:defaultValueType was complicating things and one of the reasons it was
introduced is to disambiguate the values of sh:constraint.
With this change every predicate can have only one possible type now
and sh:defaultValueType is no longer needed

Best,
Dimitris

-- 
Dimitris Kontokostas
Department of Computer Science, University of Leipzig & DBpedia Association
Projects: http://dbpedia.org, http://rdfunit.aksw.org, http://
http://aligned-project.eu
Homepage:http://aksw.org/DimitrisKontokostas
Research Group: AKSW/KILT http://aksw.org/Groups/KILT