Create CSDL model that is used for all examples

[ralfhandl]

Some of our examples require to know whether a property is structural or navigation, or which type it has. We sometimes mention this in the example description, and sometimes leave it as an exercise to the reader.

Proposal

Alternatives:

1. Add consistent example model to CSDL chapter 16, or
2. Enhance one of the existing example models to cover all examples, and adjust the examples to keep the model as brief as possible, or
3. Add text to all examples describing the model elements used in the example "code"