RFR: JDK-8239817 Eliminate use of contentContainer and friends

[Jonathan Gibbons]

Please review a moderately simple update to remove the use of `<div 
class=contentContainer>` and other similar elements from the generated 
pages.

The styles associated with contentContainer and friends are moved to the 
immediately enclosing <main> element, which means they can also be 
removed from the .header class, used for the main page heading.

There should be no visual change when the pages are viewed in a browser: 
the main content of each page has the same layout and margins as before, 
but with less HTML and CSS.

Notes:

The source code changes are generally all about removing the code to 
create an enclosing <div> element.  Generally, the content that was 
previously added into the <div> is now added directly into the container 
to which the div was previously added.

In the HtmlStyle class, the *Container entries are no longer required 
and have been removed.  Two additional unused members have also been 
removed.

In the stylesheet, the entries for the list elements leverage the 
recently added "notes" class and use the ">" construction, as in  
"dl.notes > dt". This construction ensures that the style only applies 
to the immediately enclosed dt (or dd) element, and not to any more 
deeply nested element. This is both semantically better and more 
efficient as well.

In the tests, the most notable changes are in TestModules.java. Many of 
the test cases there are bimodal, and check for the presence or absence 
of strings depending on the command-line options. In these test cases, 
it was not enough to remove instances of '<div 
class=\"contentContainer\">' ... it had to be replaced with what 
preceded it, to verify that not intervening text was being incorrectly 
generated.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8239817
Webrev: http://cr.openjdk.java.net/~jjg/8239817/webrev.00/index.html