Add to several playslits

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In spotify and YouTube you have the possibility to click on a song and add it to several playlist in the same time. (And remove from one of it if you want) it's done thanks to a checklist. 

It could be very  nice because it's fast and if you miss click you don't have to go to the right playlist to remove the song. 

Furthermore this option will allow to know, by clicking on it, if it is in a playlist and which one thanks to the checklist. It's very useful when you want to know if you have already keep the song. And if you want to change some of its location

The example is in the picture

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