Return an error when fetching a URL returns an HTTP error.

The error never makes it back to the use (it's always returned in a
task), but at least it gets logged…

Fixes #66.
Revert back to 21a87d8 "Add google analytics."
Ignore errors about the missing FeedInfo.ArticleKeys field.

We can revert this commit once all of the FeedInfos have been rewritten without this field.
Add Article.WhenAdded.

This field is the time when the article was put into the datastore. It
is used to determine which articles are "Latest," but it is not
displayed on the web pages; the article's publication date is
displayed on the web page.
Change the latest threshold from 18 to 24 hours.
Merge pull request #151 from eaburns/dev/eaburns

Return an error when fetching a URL returns an HTTP error.
Merge pull request #153 from eaburns/dev/fixit

Revert  all broken commits.
Fix index.yaml.