Add the option to duplicate episodes in the same podcast

[brandonhundt]

I am splitting this use case off of #981.

There are use cases when a producer wants to republish an episode from the archive within the same podcast. In a Publish to Feeder walkthrough, Snap Judgement asked if they could "republish" an older episode from their feed.

I think we should give producers the option to "duplicate an episode" (ala Augury Flights). It would copy the same audio files and episode data over to a new DRAFT episode in the same podcast, under a new GUID.

Note: There might be an issue with previously existing drafts and faked-in ads targeted specifically to a draft, so replacing a draft with a different draft of a dupe episode might cause Ad Ops headaches.

Here's a very rough sketch of where in the UI this should be tucked away...

I might be overlooking things here, in terms of what should be duplicated and what shouldn't.