feat: Add Share option for artists, albums, and tracks

This feature is only available on the Subsonic media provider. Using a
Jellyfin server will make Supersonic hide the "Share" option.

* Artists: Option available in grid view and in Artist view.
* Albums: Option available in grid view and in Album view.
* Tracks: Option available in tracklist, when a single track is selected.

ui/browsing/playlistpage.go

@@ -87,10 +87,12 @@ func newPlaylistPage(
 		conf.TracklistColumns = cols
 	}
 	_, canRate := a.sm.Server.(mediaprovider.SupportsRating)
+	_, canShare := a.sm.Server.(mediaprovider.SupportsSharing)
 	remove := fyne.NewMenuItem("Remove from playlist", a.onRemoveSelectedFromPlaylist)
 	remove.Icon = theme.ContentClearIcon()
 	a.tracklist.Options = widgets.TracklistOptions{
 		DisableRating: !canRate,
+		HideSharing:   !canShare,
 		AuxiliaryMenuItems: []*fyne.MenuItem{
 			util.NewReorderTracksSubmenu(a.doSetNewTrackOrder),
 			remove,