Added features

[Rodrigap]

I love that you added some extra features to this! The removal of the playlist tracks from the search results, as well as the ability to search on enter, makes your app a lot more user friendly. There's a couple of minor bugs in the first new feature, like that the song is only returned to the search results when you delete the song from the playlist and perform another search. Also, when you perform another search, you can add duplicate songs to the playlist because you never actually check to make sure that the song doesn't exist in the playlist before adding it

[Alrefai]

The removed song from playlist is pushed back to the end of the search results. I understand that this is probably not a good design choice. But it is not easy to return the song to its original location in search results. Also, I think that returning the song to top of the search results in not a good choice either.

I thought about hiding the the ' + ' sign when a song is added to playlist. However, this require more code alternation. Moving the song between lists was easier to implement. I will think about a better solutions later.

The bug that add duplicate songs to the playlist is fixed. See below commit:
470eb6d