Download feed image to feed data directory

- FeedReader.image_path is undefined when no image available, otherwise
  contains local path for feed image
- Part of enhancement for issue #2
Store feed image width/height
Add feed image to menu when available

- Needs some better scaling/styling to be applied
Restyle menu title

- Title on top
- Icons for feed actions beneath
- Works much better when feed title images are used
Remove menu separator

- Will use separator to separate different feeds