Make DZFileStream instances single map to URL.
Add some images.
1. add images for feed list item bullet (playing/new/half played).
2. add an UIImage category to manage template images, and render transparent template images.
3. add 'Download button' images (download/pause/finished), and an empty view class for it.
4. move view controller classes to view controller group, gui element classes to gui group.
5. remove highlighted button images, no need now, use transparent template images instead.