Feature: Content creator channels

Had a request to be able to mark decks as "featured on such-and-such a stream" by content creators. Current idea:

• Allow users to create content "channels" (could be a blog, video stream, podcast, etc.)
  • Can set users to as contributors, or revoke their own contributor status for the channel (as long as they aren't the last one)
  • Channels should have landing pages where a description of the channel lives, along with a list of the contributors, and a deck listing of decks that have been featured on that channel
  • Meta: name, description, general URL
• Channel contributors can link any public deck to their channel with an arbitrary URL. This will show up in the deck sidebar as "featured on [channel name]" linked to the URL (so for instance a channel could link to the specific video where the deck was played)
  • Channel linkage should be tagged at a specific snapshot ID so that the system can distinguish between links to the current public version and links to past versions
• Homepage should show a list of channels in the sidebar, ordered by activity (based on timestamps for decks that have been associated, maybe?)
• Need moderation tools for admins:
  • Add or remove contributors to a channel
  • Modify channel title or description
  • Close/delete the channel (thus disabling all channel linkage across the site for that channel)
  • Add or remove channel links for specific decks

No files, tests, or entry points are named. Start by locating the existing user, deck, snapshot, homepage, and admin API surfaces, then determine how channels, contributors, snapshot-specific links, landing pages, activity ordering, and moderation fit together. Done means the complete channel workflow and its moderation controls are implemented and tested.