RFR: JDK-8242326: use new "summary-list" CSS class instead of general "block-list" for list of summary sections

[Jonathan Gibbons]

Please review the latest in the series of updates to change uses of CSS 
class `block-list` to use separate class names.  This is for the list of 
summary sections that appear on most declaration pages.

The pattern is much the same as before, so I won't go into a lot of 
details.  As before, the changes percolate  from the builder classes to 
the writer classes to the writer-impl classes.

Some of the changes are cosmetic, updating the doc comment, and updating 
the name of parameters and local variables to better reflect their usage.

There's one more similar change in the pipeline, for the summary tables. 
When that has been done, I'll do another round of update on the comments 
in HtmlStyle.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8242326
Webrev: http://cr.openjdk.java.net/~jjg/8242326/webrev.00/
API: http://cr.openjdk.java.net/~jjg/8242326/api.00/