Index file for applet demos should be part of the workspace and demos zipfile

The Java Plug-in demos are part of the Hopper workspace and are
posted on the web with the release. However, the index file for the
demos (applets.html) is only available on the web. This file should
be checked into the workspace in two places...

demos/applets.html (for applet tags)
demos/plugin/applets.html (for object/embed tags)

Also, this file needs to be updated to include all the demos that
are posted. In addition, this file should be included in the demos.zip
file that is created as part of the build. (See Release.gmk)

Fixing this bug will prevent us from having to manually get this file
prepared at release or test time.