Context menu and additional actions for podcast view

[NattyNarwhal]

These aren't terribly reactive.

Probably just add the API endpoints we don't support yet:

• refreshPodcasts
• createPodcastChannel
• deletePodcastChannel
• deletePodcastEpisode
• downloadPodcastEpisode

I don't think any of the other common library ops (other than play/append) make sense.