Chapter 7.1.2 - rework "Thing Model" to new title/content "Instance descriptions and class models"

[mlagally]

Chapter 7.1. should contain a section called "Instance descriptions and class models"

This is an introduction to the concepts, i.e. descriptive documents to describe a class of things and instances.
Explain that we have a modeling language and a description for individual instances.
Devices can be self descriptive, i.e. carry their TD.