Fix cover download

Old url wasn't any longer usable

Signed-off-by: Littlesat <littlesat99@yahoo.com>
MerlinMusicPlayer: Fix cover search issues

- If hardware decoding was disabled and album field in mp3 tag
 was empty, "n/a" was used for cover search.
- When album field is empty now title is used for cover search.

Signed-off-by: Littlesat <littlesat99@yahoo.com>
MerlinMusicPlayer cover download improvments

- Try to download medium size covers at first. If no covers were found
search without size restriction.
- Use not original file name from URL, because some services use same
filename for different covers. This prevents showing wrong covers.

Signed-off-by: Littlesat <littlesat99@yahoo.com>