FILE_SAVE: Refactor data save, so data can be saved without the dialog
           box.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Load main profile:
  - make sure that when capture is selected, it started right away
    (needed for testing)
  - make sure it's the last thing saved, so things are set up
    when it's loaded
  - add a few keywords:
     - cycle = <n> cycle through the main loop n times
     - save_png = <f> save the png as file <f>

Now, you can (manually) add things like:
[Capture_Configuration]
cycle = 500
capture_started = 1
cycle = 50
save_png = foo.png

and it saves the foo.png file.

Signed-off-by: Robin Getz <robin.getz@analog.com>