Add new method for updating songs based on song ID

Show status updating database.

Fixes #750

src/playlist/playlist.cpp

@@ -797,7 +797,7 @@ bool Playlist::dropMimeData(const QMimeData *data, Qt::DropAction action, int ro
     InsertSmartPlaylist(generator_data->generator_, row, play_now, enqueue_now, enqueue_next_now);
   }
   else if (const InternetSongMimeData *internet_song_data = qobject_cast<const InternetSongMimeData*>(data)) {
-    InsertInternetItems(internet_song_data->service, internet_song_data->songs, row, play_now, enqueue_now, enqueue_next_now);
+    InsertInternetItems(internet_song_data->service, internet_song_data->songs.values(), row, play_now, enqueue_now, enqueue_next_now);
   }
   else if (const RadioMimeData *radio_data = qobject_cast<const RadioMimeData*>(data)) {
     InsertRadioItems(radio_data->songs, row, play_now, enqueue_now, enqueue_next_now);

src/playlist/playlistbackend.cpp

@@ -214,7 +214,7 @@ QList<PlaylistItemPtr> PlaylistBackend::GetPlaylistItems(const int playlist) {
 
 }
 
-QList<Song> PlaylistBackend::GetPlaylistSongs(const int playlist) {
+SongList PlaylistBackend::GetPlaylistSongs(const int playlist) {
 
   SongList songs;
 
@@ -230,7 +230,7 @@ QList<Song> PlaylistBackend::GetPlaylistSongs(const int playlist) {
     q.BindValue(":playlist", playlist);
     if (!q.Exec()) {
       db_->ReportErrors(q);
-      return QList<Song>();
+      return SongList();
     }
 
     // it's probable that we'll have a few songs associated with the same CUE so we're caching results of parsing CUEs

src/playlist/playlistbackend.h

@@ -76,7 +76,7 @@ class PlaylistBackend : public QObject {
   PlaylistBackend::Playlist GetPlaylist(const int id);
 
   QList<PlaylistItemPtr> GetPlaylistItems(const int playlist);
-  QList<Song> GetPlaylistSongs(const int playlist);
+  SongList GetPlaylistSongs(const int playlist);
 
   void SetPlaylistOrder(const QList<int> &ids);
   void SetPlaylistUiPath(const int id, const QString &path);