First working version with cover manager.
- Recycling fixed
- Android httpclient leak fixed

Seems fast enough.
Cover Manager improve: add priority
- Add priority to always process requests from the nowplaying fragment
- Discard all web requests when MAX requests
Fix cover manager
- Fix concurrency problems by putting the listeners inside the coverinfo
- Fix bitmap sharing problem with recycling (make a copy first)
- Discard non matching notifications for the cover not found event
Little robusteness improvements
Little robusteness improvements :
- Add a way to stop the cover executors
- Do not process requests without album or artist
Little robusteness improvements :
- Prevent Null pointer exception
- Use the enableAlbumArtLibrary property to enable/disable the cover web fetching from the playlist fragment.
- Minor improve not to regroup requests with different priority or retrievers
Fix for #286 : Crash whith java.util.ConcurrentModificationException on PlaylistFragment
Fix for #286 : Crash whith java.util.ConcurrentModificationException on PlaylistFragment
Remove the updating hack
Merge pull request #288 from jcnoir/cover

Multithreaded Cover Management