Every aggregating sidebar had the same code repeated over and over, and no aggregating sidebars handle errors in an intuitive manner. This patch adds an Aggregator class that encapsulates all of the feed handling, including (bad) Atom support and decent error reporting. Other feed based sidebar models can use the Aggregator as a superclass to reduce code duplication.

This patch additionally provides an AggregationController sidebar that will render any arbitrary RSS/Atom feed.

The Flickr and 43Things sidebar models were converted to use the Aggregator as a superclass because they had unit tests, and they were easily tested in a running Typo instance by the patch author.

Errors should be reported in the admin console, but getting them into the application log is a start.