[macOS][iOS]: Continuous Playback "Append Mode"

[Grant Davis]

I would like to be able to configure Continuous Playback playlist so that once it is generated, it will only suggest new episodes at the bottom of the playlist as episodes are pulled out of it for playback.

Currently, the app will maintain an order where episodes will be replaced with episodes from the same podcast if it has higher priority than other podcasts. I would rather be able to get through a list of what is shown and just have new episodes added to the end as I listen to episodes or pull them out.

Tasks:

• Add setting to continuous playback to change modes
• Sync new setting in iCloud preferences (not database)
• Update ContinuousPlaybackModel with new logic to handle different settings. Refactor to handle different configurations easily for more updates to these.
• Add tests for new model settings
• Update iOS interface with setting option
• Update macOS interface with setting option

Questions:

• Should there also be a refresh button for continuous playback to force a refresh in case the append mode is stale and the user wants to see the latest?
  Probably, yes. Makes sense.