Set the cover tags only from the CoverAsyncHelper to improve robustness
--> Avoid inconsistencies between cover request and tag.
Fix #343 : "Go to Artist" searches forever with AlbumArtist option set
Revert "Fix #343 : "Go to Artist" searches forever with AlbumArtist option set"

This reverts commit 3dcf2f1e6570bb26601222772a294862746ddff4.
Fix #343 : "Go to Artist" searches forever with AlbumArtist option set
- Update the goto artist from nowplaying screen to use the albumArtist if this option has been set in MPD.
- Hide the progress bar even if no result (but display a no result text view in this case)
Fix #343 : "Go to Artist" searches forever with AlbumArtist option set
- Fix : the noresultview was displayed with non empty results.
Process the onCoverDownloadStarted message (to display the progress bar) only if the cover key does match the cover view key.
Avoid crash : adapter has changed but ListView did not receive a notification

 java.lang.IllegalStateException: The content of the adapter has changed but ListView did not receive a notification. Make sure the content of your adapter is not modified from a background thread, but only from the UI thread. Make sure your adapter calls notifyDataSetChanged() when its content changes. [in ListView(16908298, class com.mobeta.android.dslv.DragSortListView) with Adapter(class com.mobeta.android.dslv.DragSortListView$AdapterWrapper)]
            at android.widget.ListView.layoutChildren(ListView.java:1555)
            at com.mobeta.android.dslv.DragSortListView.layoutChildren(DragSortListView.java:2136)
            at android.widget.AbsListView.onLayout(AbsListView.java:2091)
Remove synchronization on update()
To be tested.