Add individuals to the schema

[tgoprince]

I propose we extend the schema so that we can also exchange objects referring to individuals.

For instance:

{
  "type": "Instance",
  "id": "1",
  "name": "john",
  "description": "This is John!",
  "types": [
    {
      "type": "Class",
      "id": "person-class"
    }
  ],
  "propertyAssignments": {
    "name": "John Doe",
    "age": 30,
    "dataOfBirth": "2000-01-01"
  }
}

Where:

• types is an array of reference objects pointing to the types an individual instantiates.
• propertyAssignments contain the instantiation of attributes

I'm not sure how to handle the instantiation of relations...