Core reference and Libraries reference entries share the same template

Because there's a single template to build all of the reference pages, the Library reference pages have the wrong left-nav option selected (Reference and not Libraries). Also, they can't have a custom message at the top of the page about the Javadoc. I think this requires digging into java-generate and rebuilding the Java classes.

In addition, the non-core Libraries from the Processing Foundation (Video and Sound) can't have a separate header message. They link to the Libraries Javadoc, but the code isn't there. Thinking about this more, we could probably build those Javadocs and add them while the rest are built.

Empieza examinando la plantilla compartida de páginas de referencia y el punto de entrada java-generate mencionado en el issue; después, sigue el proceso mediante el que se vuelven a generar las clases Java. Se considera terminado cuando las páginas de Library seleccionan Libraries en la navegación izquierda, admiten mensajes Javadoc personalizados y las páginas Video y Sound gestionan sus enlaces de Javadoc o los Javadocs generados según lo previsto.