Adding multiple time the same property in the @reverse property should raise an error

[joke1196]

The Reverse model takes a list of properties as in put, this list should not contain twice the same property.
e.g.

@reverse: {
"namespace:dataset":{"@id": 1},
"namespace:dataset":{"@id": 2},
}

As we cannot decide which one is the correct field we should raise an error.
The user is responsible of generating the list of entities in the @reverse property

Acceptance criterias:

• The instanciation of a Reverse instance should throw an IllegalArgumentException when a property is found twice in the list of properties passed as parameters
• The Reverse model still can only holds a list of tuple: properties to JsonLD. The JsonLD can be an array of JsonLDEntities or a single JsonLDEntity. If the JsonLD is anything else; the Reverse instanciation should still throw an IllegalArgumentException