Standardize background colors to light green or light red in several places:
* Modqueue positive/negative score backgrounds.
* Modqueue quality/sample warning backgrounds.
* User feedback positive/negative backgrounds.
* Ban expired/unexpired backgrounds.
* Flag resolved/unresolved backgrounds (removed; resolved flags no
longer have a grey background because of inconsistencies in what
resolved means).
Don't remove the bottom margin from all <p> elements in tables. Instead
remove it only from the last element in dtext blocks. This way we don't
have to also kludge <blockquote> padding to work with zero-margin paragraphs.
Better fix for #1655.