Add History (plus Mark as Played) support for "add by Custom RSS feed" podcasts

[freekvh]

Is your feature request related to a problem? Please describe.
I'm always frustrated when one of my fav podcasts which has a custom url (because it is a paid subscription) does not mark played episodes as played.

Describe the solution you'd like
I would like any episode I have played to be marked as played. And a "mark all as played" would be nice so for news podcasts one does not have the entire out-of-date backlog marked as "unplayed".

Describe alternatives you've considered
Remove listened episode from the list entirely? Actually I would like to have both: Hide all played episodes, that keeps things clean ( I made a separate issue for this #1241).

[mitchdowney]

@freekvh this is part of a big feature gap between how "add through Podverse search engine" and "add by custom RSS feed" podcasts are handled. Basically add by custom RSS feed podcasts lack many of the features than the podcasts maintained on our server-side. Adding more equal feature support for custom RSS feeds will require a lot of work, including many front-end interactions, and updates to our database schema and API. We'd love to add support for this, but it may not be present until next generation v5 Podverse, which we don't have a time-table or the resources to do at the moment (Creon and I both have day jobs, and we still spend more money on Podverse than revenue we take in). We're hoping we can get funding for Podverse some day to hire more help with our giant sprawling architecture...