Copy user additional states when no provider/equation is known.

src/main/java/org/orekit/overview.html

src/main/java/org/orekit/propagation/AbstractPropagator.java

src/main/java/org/orekit/propagation/Propagator.java

src/main/java/org/orekit/propagation/SpacecraftState.java

.../org/orekit/propagation/analytical/AdapterPropagator.java

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

...propagation/integration/AbstractIntegratedPropagator.java

...g/orekit/propagation/integration/IntegratedEphemeris.java

src/site/apt/architecture/propagation.apt

src/site/apt/index.apt

src/site/xdoc/changes.xml

.../orekit/propagation/analytical/AdapterPropagatorTest.java

...orekit/propagation/analytical/TabulatedEphemerisTest.java

...orekit/propagation/numerical/NumericalPropagatorTest.java