Store feed metadata

[aaronpk]

Feeds include additional data such as a name, image and description. In the case of podcast feeds, the podcast artwork is a critical component of the feed and should be presented when viewing entries from the feed.

XRay will need to return podcast artwork as author info first.

Aperture should also add the concept of feed-level name/photo/description in order to enhance the display in readers. Here is the current proposal for adding this to Microsub: indieweb/microsub#13