Merge remote-tracking branch 'origin/develop' into develop

pom.xml

src/changes/changes.xml

...org/orekit/estimation/sequential/AbstractKalmanModel.java

src/main/java/org/orekit/files/ilrs/CRDParser.java

src/main/java/org/orekit/propagation/analytical/tle/TLE.java

...g/orekit/propagation/conversion/TLEPropagatorBuilder.java

src/site/markdown/downloads.md.vm

src/site/markdown/faq.md

src/site/markdown/release-guide.md

...org/orekit/estimation/sequential/KalmanEstimatorTest.java

src/test/java/org/orekit/files/ilrs/CRDParserTest.java

...t/java/org/orekit/propagation/analytical/tle/TLETest.java

...a/org/orekit/propagation/conversion/TLEConverterTest.java

src/test/resources/ilrs/lageos1-test.npt