Blog page performance changes

Makes webpages much smaller by limiting the number of other blogs listed in the sidebar and compressing whitespace in the html that doesn't change its meaning.

Provides full index pages for blogs, since the sidebar only shows a few entries at a time.

Improves cacheability changing the url space for blogs to allow filtering by topic using a URL segment rather than by querystring. This entailed adding a slug to the secondarytopic snippets to be used as the value for that URL segment. Note that the current implementation still uses 'topic=' in a querystring, but the request is efficiently redirected to a cacheable page.

Changes the filters on blog pages to filtering only on a topic (as opposed to a primary or secondary topic). The "News" primary topic was preserved as one of these topics. The other primary topics have been removed.