Add content sources download report

So, not trying to predict the future here but wanted to collect and return information that I would be useful beyond just the counts of downloads per source.  While we're at it.

The *total_passes* is really an indicator of how efficient the defined content sources are.  Ideally, the number of passes should not be > 2.  Any more and the container is having to try too many sources and getting too many failures.  Suggests some of the sources need to be removed, re-defined or re-prioritized.

The difference between *total_sources* and the # of sounces listed in the *downloads* helps show the percentage of the available sources used.  If we consistently report that only 3/20 sources provide content that users want to download, users may want to rethink how they have their content sources defined.

Finally, I think it's useful for users to see the *total_failed* counts per source.  Download failures indicate a disconnect between what's in the catalog of available content and what the source actually seems to provide.