Merge branch 'issue-534' into release-9.3

pom.xml

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

src/main/java/org/orekit/time/GPSDate.java

src/site/markdown/downloads.md

src/site/xdoc/changes.xml

src/test/java/org/orekit/Utils.java

...orekit/propagation/analytical/gnss/GPSPropagatorTest.java

src/test/java/org/orekit/time/GPSDateTest.java