Merge branch 'issue-498' into develop

pom.xml

src/main/java/org/orekit/errors/OrekitMessages.java

...surements/modifiers/AngularTroposphericDelayModifier.java

...rements/modifiers/RangeRateTroposphericDelayModifier.java

...easurements/modifiers/RangeTroposphericDelayModifier.java

...ation/measurements/modifiers/TroposphericDSConverter.java

...s/modifiers/TurnAroundRangeTroposphericDelayModifier.java

src/main/java/org/orekit/frames/TopocentricFrame.java

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

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

...rg/orekit/models/earth/ViennaModelCoefficientsLoader.java

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

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

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