Make examples consistent and comprehensive

[dr-shorthair]

We have a set of example RDF files that partially illustrate the scope and capabilities of the Ontology.
Some of them are included inline in the document.
These must be made consistent and reasonably comprehensive.

Supersedes
#246
#204
#159
#118

Work in this branch: https://github.com/w3c/sdw-sosa-ssn/tree/update-examples-2

I will copy the key concerns of the old issues here and close them.

[dr-shorthair]

Prefix consistency: #246 (comment)

Extended examples in Appendix

Collections #159

SensorThings STA example #118