Fixed SpotBugs warnings.

spotbugs-exclude-filter.xml

src/main/java/org/orekit/attitudes/AttitudesSequence.java

src/main/java/org/orekit/estimation/measurements/PV.java

...ain/java/org/orekit/estimation/measurements/Position.java

...timation/measurements/modifiers/DynamicOutlierFilter.java

.../orekit/estimation/sequential/UnivariateProcessNoise.java

src/main/java/org/orekit/gnss/antenna/SatelliteType.java

src/main/java/org/orekit/gnss/attitude/GPSBlockIIA.java

src/main/java/org/orekit/gnss/attitude/GPSBlockIIF.java

src/main/java/org/orekit/gnss/attitude/GPSBlockIIR.java

src/main/java/org/orekit/gnss/attitude/Galileo.java

...a/org/orekit/models/earth/EstimatedTroposphericModel.java

.../java/org/orekit/models/earth/FixedTroposphericDelay.java

...a/org/orekit/models/earth/GlobalMappingFunctionModel.java

src/main/java/org/orekit/models/earth/MappingFunction.java

src/main/java/org/orekit/models/earth/MariniMurrayModel.java

src/main/java/org/orekit/models/earth/MendesPavlisModel.java

...va/org/orekit/models/earth/NiellMappingFunctionModel.java

src/main/java/org/orekit/models/earth/SaastamoinenModel.java

src/main/java/org/orekit/models/earth/ViennaOneModel.java