Merge pull request #4248 from abika/master

Fix for saving the playlist multiple times when adding files to it
Add an option to sort Grooveshark playlist alphabetically. Fixes issue #3480.
Did it the lazy way for now, but it would have better to refactor Grooveshark code, to add a proper sort model, etc.
Grooveshark: don't crash when receiving the reply for a canceled request.
Mark all tasks as finished when removing all items, to prevent never ending task in case we disconnect or refresh before all replies have been received.
More efficient load of local files.