[Feature request] Playlist support

[quidnu]

Please add playlist support. Many video collections of interest are organized in playlists and not channels. I don't know if the identifier for playlists is in a different namespace. yt-dlp support playlists.

[NotJoeMartinez]

This is something I want to add but presents a design problem. Every video in the playlist needs to be connected to a channel, and If one of the videos in a playlist is already saved in the database it will error out asking the user to "update" the channel if the channel already exists in the database.

So for our download playlist mode we need to bypass this error checking for duplicate channels

[NotJoeMartinez]

Added in #139, available on v0.1.44