Better sorting of comments and downtimes

This fixes a few things mainly adding the ability to sort the comments
and downtimes on the host and service pages. There were also a few style
changes I made as I saw fit along the way.

Mostly, the style changes were just wording tweaks, capitalization and
formatting. Added output to show current sorting method by default. This
may not be desired but I liked it so I kept it. Can remove it if people
do not like it.
Do not display sort order by default

Only display the sort order when it is not the default. Small HTML
fixes to prevent having an empty DIV for no reason.
Merge pull request #338 from awiddersheim/fix_comment_downtime_sorting

Better sorting of comments and downtimes