Synchronized field propagation with primitive double propagation.

.../java/org/orekit/propagation/FieldAbstractPropagator.java

.../org/orekit/propagation/FieldAdditionalStateProvider.java

...ekit/propagation/FieldAdditionalStateProviderAdapter.java

...n/java/org/orekit/propagation/FieldClosedFormAdapter.java

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

.../java/org/orekit/propagation/FieldStackableGenerator.java

...agation/analytical/FieldAbstractAnalyticalPropagator.java

...gation/integration/FieldAbstractIntegratedPropagator.java

...opagation/integration/FieldAdditionalEquationAdapter.java

...kit/propagation/integration/FieldAdditionalEquations.java

...kit/propagation/integration/FieldIntegrableGenerator.java

...kit/propagation/integration/FieldIntegratedEphemeris.java

...propagation/integration/FieldAdditionalEquationsTest.java

...propagation/integration/FieldIntegrableGeneratorTest.java

...propagation/integration/FieldIntegratedEphemerisTest.java

...t/propagation/numerical/FieldNumericalPropagatorTest.java