RFR: 8233866: Text in table cells has inconsistent alignment

[Hannes Wallnöfer]

Please review:

JBS: https://bugs.openjdk.java.net/browse/JDK-8233866
Webrev: http://cr.openjdk.java.net/~hannesw/8233866/webrev.00/
API docs: http://cr.openjdk.java.net/~hannesw/8233866/api.00/

This is a tiny tweak in the definition of the „block“ CSS class that sets its top margin to zero and adds the same amount of space to the bottom margin instead. 

This causes the right-most „description“ column in most javadoc tables to have the same vertical alignment as the other columns (at least as close as I could get without changing major aspects such as fonts or font sizes) while retaining the spacing and layout of the table.

The other significant visible change is that in index pages the (secondary) <dd> lines are now closer to the <dt> element they belong to, instead of the following <dt> elements. I think this is a welcome change as well.

Thanks,
Hannes