1. Add CartesianProductEJA.

2. Check the axioms in the constructor when check != False?

3. Add references and start citing them.

4. Implement the octonion simple EJA.

5. Factor out the unit-norm basis (and operator symmetry) tests once
   all of the algebras pass.

6. Add a TrivialEJA class and use it in the tests for is_trivial().
   The random_eja() function should also be able to return these.