Removed duplicated code in measurement creators for OD tests.

src/test/java/org/orekit/estimation/Context.java

src/test/java/org/orekit/estimation/DSSTContext.java

src/test/java/org/orekit/estimation/StationDataProvider.java

src/test/java/org/orekit/estimation/TLEContext.java

...kit/estimation/leastsquares/DSSTBatchLSEstimatorTest.java

...ekit/estimation/leastsquares/TLEBatchLSEstimatorTest.java

.../estimation/measurements/DSSTRangeMeasurementCreator.java

...imation/measurements/DSSTRangeRateMeasurementCreator.java

...org/orekit/estimation/measurements/DSSTRangeRateTest.java

...ava/org/orekit/estimation/measurements/DSSTRangeTest.java

...ekit/estimation/measurements/RangeMeasurementCreator.java

.../estimation/measurements/RangeRateMeasurementCreator.java

...t/estimation/measurements/TLERangeMeasurementCreator.java

...timation/measurements/TLERangeRateMeasurementCreator.java

.../org/orekit/estimation/measurements/TLERangeRateTest.java

...java/org/orekit/estimation/measurements/TLERangeTest.java

...orekit/estimation/sequential/DSSTKalmanEstimatorTest.java

.../orekit/estimation/sequential/TLEKalmanEstimatorTest.java