Fix Javadoc generation and links for the site - Removed `maven-jxr-plugin` - Generating no Javadoc JARs (this was already the case) - Removed Javadoc JARs from the assembly in `log4j-distribution` - Generating Javadoc HTML only for `log4j-core` and `log4j-api` - Copying generated Javadoc HTML to `target/site/javadoc/<artifactId>`