Comment 6 for bug 1393749

Fix for iTunes, Browse, external libraries and dragging a file from the file browser to a deck.
https://github.com/mixxxdj/mixxx/commit/58722db4561d325f4ec58f342395752a3187a10e

Drag and drop from the track-table to the sidebar or from a file browser to the sidebar or track table is slightly harder (the fix comes with a performance penalty in the main thread). I think since we already do the bulk add of the tracks (including parsing their metadata) on the main thread in TrackDAO::addTracks, the cost is not that high to make it take longer but I still feel iffy about it.