Add `publish-threshold` for videos widget to only display videos published in the last `n` days

[drejleeo]

I would like to only display videos that were published in the last n days rather than have all older videos. For me, this comes in handy when aggregating multiple channels that publish videos in certain time periods and exclude what I don't really need anymore to have a clean, tidy interface - when there is nothing to do, there is nothing to do.

Since I had made the changes, I thought that other people might want this as well.

Thanks! :)

Important

If this gets approved, I would like to have someone test the feature as well as this is my first time dwelving in Go lang.