Use albumartist in DatabaseCommand_AddFiles

So far, the album database uses the track artist. This changes it to use the album artist if one is available.
Merge pull request #274 from justin-time/master

Update for the Download Tomahawk section.
Automatic merge of Transifex translations
Updated README.
README style.
Fixed TWK-1779: Duped script-collection tracks.
Make readCallback a member function
Make readDoneCallback a member function
Make QNR_IODeviceStream thread-safe
Automatic merge of Transifex translations
Sort album models by artist name first.
Make sure album grid on collection page is sorted.
Updated ChangeLog.
Renamed LoadXSPFDialog to LoadPlaylistDialog.
Renamed importXSPF to importPlaylist in ActionCollection.
Renamed importXspfPath to importPlaylistPath in TomahawkSettings.
Style fixes for M3uLoader.
Support loading m3u playlists from 'Import Playlist' dialog.
Updated ChangeLog.
Finish loading in RecentlyPlayedModel when there's no history to be found.