Disallow I on concepts without equivalence defined.

[hanjoosten]

With the introduction of TTYPE, we now have concepts without a proper equivalence relation defined. This already causes errors, because SQL does not allow these concepts as the primary key in a concept table. (i.e. BINARY, FLOAT)

As a consequence, certain properties must be disallowed on relations with such concepts as source or target.

@sjcjoosten, @WolframKahl, could you give your opinion about this? I have discussed this today with @stefjoosten, and we agreed to call for the help of the mathematicians 8-))