support for shape definition and generation

[mchlrch]

Implement support for defining and generating basic SHACL shapes.

Dependencies in the grammar:

• mappings and shapes both depend on vocabulary
• no dependency from mappings to shapes (yet)

See also:

• https://w3c.github.io/shacl/shacl-compact-syntax/
• https://www.topquadrant.com/technology/shacl/shacl-compact-syntax-quick-tutorial/
• https://www.w3.org/TR/shacl/#shacl-example

[mchlrch]

First iteration of the prototype is done. Describing basic shapes works.

Sample: https://github.com/zazuko/rdf-mapping-dsl/tree/issue_115_shapes/runtime-EclipseXtext/person-shapes

Installation instructions and limitations: https://github.com/zazuko/rdf-mapping-dsl/blob/issue_115_shapes/README-shapes.md