RFR: 8219733: Restore javadoc header styles

[Hannes Wallnöfer]

Please review:

Issue: https://bugs.openjdk.java.net/browse/JDK-8219733
Webrev: http://cr.openjdk.java.net/~hannesw/8219733/

This restores the visual appearance in javadoc pages and makes the stylesheet easier to understand by using the new page type classes in body elements.


The following selectors are used for italic h2 headers:

body.class-declaration .summary h2,
body.class-declaration .details h2,
body.class-use h2,
body.module-declaration .blockList h2 

These selectors are used for darker grey background h3 headers:

body.class-declaration .summary h3,
body.class-declaration .details h3

In the case of class-declaration and module-declaration pages which can contain user-provided text content I used additional intermediate classes to limit the selectors to the intended sections.

Thanks,
Hannes