Add to @context, create example bob and lynn jsonld.

Please don't merge if you don't like the changes to @context: I changed Person and Group to foaf, for example, just to move in that direction, left the others as vf. Everything else I added is used in our example.

The example covers Bob, me, Mikorizal, Sensorica, and our relationships. It has its own context for now. (Easier to do as PR, no separate workflow.)

Both files compile in jsonld playground.