javadoc of modules

[Remi Forax]

For the JDK, there are several kind of modules from a doc perspective,
we have root modules that are available by default, like java.base,
we have implementation modules, those that starts with jdk like jdk.jshell,
and we have modules that are not root modules, i.e. available if you use --add-modules, like java.xml.bind.

I think that the javadoc panel that display the avaialble modules, should
- separate the different kind of modules, java.xml.bind should not be mixed with java.base if it will not be present in Java 10
- have a way to see implementation modules and their corresponding javadoc.

regards,
Rémi