Streamline Podcast handler code with a POSO

[chickdan]

I wanted to make the code-base a little more Swifty so I created a Podcast object and incorporated some json serialization to make the code a little more streamlined.

I don't know how to test this as there doesn't seem to be a repo for the Forem app and Dev-ios is deprecated as a product (if there is a repo I would love to contribute as there appears to be a theming issue with the status bar and bottom toolbar). So if you find anything please let me know, this is experimental in the meantime. If all goes well I can open PRs for other objects, thanks!