Minor fixes before merging issue-712 branch into develop.

src/main/java/org/orekit/gnss/AppliedDCBS.java

src/main/java/org/orekit/gnss/AppliedPCVS.java

src/main/java/org/orekit/gnss/RinexHeader.java

src/main/java/org/orekit/gnss/RinexLoader.java

src/main/java/org/orekit/gnss/SatelliteSystem.java

src/main/java/org/orekit/gnss/TimeSystem.java

src/main/java/org/orekit/gnss/clock/ClockFile.java

src/main/java/org/orekit/gnss/clock/ClockFileParser.java

src/main/java/org/orekit/gnss/clock/package-info.java

src/main/java/org/orekit/overview.html

src/site/markdown/index.md

src/test/java/org/orekit/gnss/ClockFileParserTest.java

src/test/java/org/orekit/gnss/RinexLoaderTest.java