Allow to go to the current playlist song from the nowplaying fragment :
- Add an item in the now playing popup menu
- Add a click listener on the album cover view
Blacklist wrong cover
- A long click on the cover opens a menu with an item "Other image ..." to blacklist the current cover  image url and try to load a new one.
The cover urls and blacklisted cover urls are stored in two files in the cover directory  : covers.bin, wrong-covers.bin
These 2 files can be removed with  the clean cover cache existing method.
Merge pull request #302 from jcnoir/master

Blacklist wrong cover & Go to current playlist song