Change screenshot to better one.
Network manager improvements:

1) Remove one ":" from "image::" to fix bug (i dunnow why but
   every time I generate html file there should appear also folder
   called "images" but in this case. All *.png files from network
   manager folder were create in ":images" folder. So I removed
   ":" and now this files are in "images" folder)
2) Fix one comment.
Merge branch 'master' into simply-linux