[9] Review request: 8178015: Clarify requirement for app modules to export/open packages to javafx modules

[Kevin Rushforth]

Please review the following javadoc change:

https://bugs.openjdk.java.net/browse/JDK-8178015
http://cr.openjdk.java.net/~kcr/8178015/webrev.00/

This restores the links to the Module class that had to be removed 
during the transition period for the move of Module and Layer from 
java.lang.reflect to java.lang, and makes the requirements for running 
an application in a named module more clear. I also fixed a couple 
related typos in the modified paragraphs.

-- Kevin