[Music App] Add to playlist from the Queue view should add only the current song to a playlist

[Victor Thompson]

Currently the remix series of the music app will add the entire contents of the Queue when a user selects the "Add to playlist" action from the Queue header. Design has indicated that it would be preferable to only add the currently playing song.

To reproduce:
1. Navigate to the Albums tab
2. Select an Album
3. Tap the "Play all" button
4. Tab the Queue (playlist icon) action from the header to navigate to the Queue
5. Tap the 3 dot action drawer on the far right of the Queue page's header
6. Tap the "Add to playlist" action
7. Select or create a new playlist to add to
8. Tab the back button ("<") from the header to return to the app's main navigation
9. Navigate to the Playlists tab.
10. Select the playlist chosen in Step #7
11. Note that the entire contents of the queue was added to the playlist

Expected results: It is expected that the action in Step #7 adds just the currently playing song to the playlist viewed in Step #11.

Additionally, Design input is needed to verify if 1) the same action ("Add to playlist") should be added to the Now Playing view and 2) if the "Clear queue" action should be visible in both the Queue and Now Playing views.

[Ubuntu Phone Apps Jenkins Bot (ubuntu-phone-apps-jenkins-bot)]

Fix committed into lp:music-app at revision None, scheduled for release in music-app, milestone music-app-14.10-week-40