Docs: recommend dct:title for dcat:Resource instance names; update examples

[jgeluk]

Tracks part of #98. Align docs/examples to prefer dct:title over rdfs:label for naming instances of dcat:Resource-derived classes. Refs #98

[jgeluk]

Fixed by PR #137. The PR switches shapes to dct:title for DataProduct and Dataset and updates NodeShapes accordingly. Refs #98.