MFbed: Update the German website.

www/de/Makefile include the German docs.sgml
www/de/docs.sgml new translation
www/de/mailto.sgml link to docs.sgml
www/de/navigation.xml link to docs.sgml and the new German article section
www/de/includes.sgml link to docs.sgml
www/de/index.xsl link to the new German article section

Obtained from: The FreeBSD German Documentation Project.

Approved by: mheinen (mentor)