Add "unselect all videos" option when adding a playlist

Add "unselect all videos" option when adding a playlist.

The issue is that when adding a long list of videos the app automatically selects all videos to be downloaded. But very often we want to download just a few videos from the playlist. And because there is no "unselect all videos", we have to unselect one by one (sometimes hundreds of videos), which is a very time consuming task.

This feature is very simple to implement but is extremely necessary and useful. That is the only big flaw of the app. I would a really appreciate if you can solve it.

Thank you.