Propagators cannot be serializable anymore, due to attitude providers.

...kit/propagation/analytical/EcksteinHechlerPropagator.java

...ain/java/org/orekit/propagation/analytical/Ephemeris.java

...rg/orekit/propagation/analytical/KeplerianPropagator.java

...propagation/analytical/EcksteinHechlerPropagatorTest.java

...java/org/orekit/propagation/analytical/EphemerisTest.java

...rekit/propagation/analytical/KeplerianPropagatorTest.java