Unit test for rotatable set, add get_cos, get_sin and recalc.

Issue @B6 : Completed a simple test sequence to prove that
the set, add, get_cos, get_sin and recalc are working, and that
the automatic lazy calculation is working properly. Unit test is
not complete yet, still rotatable::scale, angles, apply_force
and base_object::apply() tests added or enhanced.