Improve `add podcast` workflow

[everett1992]

The current workflow to add a podcast is

1. Search for the podcast,
2. See that it doesn't exist
3. Click the add podcast button
4. Find the rss feed for the podcast
5. Enter the feed

• There needs to be a way to add a podcast without searching for it ( If I know a podcast doesn't exist why would I search for it when I want to add it).
• There should be a link to add a podcast in the search result autocomplete menu.
• The add podcast view needs to have an explanation of
  • What RSS feeds are,
  • Where to find them, and
  • Links to search google/bing/ddg filetype:xml <podcast>?
• Improved feed format errors
  • If the feed doesn't have any valid episodes the user should confirm that this podcast should be added
  • If the feed is invalid (missing title or other required attributes) the error message
    should indicate that those attributes couldn't be gathered from the feed, and not place blame on the user.