Allow data filtering upon loading to be used for explicit loading.

src/changes/changes.xml

src/design/data-filtering-class-diagram.puml

src/design/data-filtering-sequence-diagram.puml

src/design/data-loaders-data-providers-class-diagram.puml

src/main/java/org/orekit/data/AbstractListCrawler.java

src/main/java/org/orekit/data/ClasspathCrawler.java

src/main/java/org/orekit/data/DataFilter.java

src/main/java/org/orekit/data/DataProvidersManager.java

src/main/java/org/orekit/data/DirectoryCrawler.java

src/main/java/org/orekit/data/FiltersManager.java

src/main/java/org/orekit/data/ZipJarCrawler.java

src/site/markdown/data/application-data.md

src/site/markdown/data/custom-filters.md

src/site/markdown/data/filtering.md

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

src/test/java/org/orekit/data/AbstractListCrawlerTest.java

src/test/java/org/orekit/data/DataProvidersManagerTest.java

src/test/java/org/orekit/data/DataSourceTest.java