[background] Remove initial fallback images

[Iain Lane]

We currently ship some sample images of cogs and a snail in u-s-s as an initial fallback for when an invalid image is selected. This was from when there was no implementation anywhere else of background switching.

We should find out what unity's default background is and set that as the fallback instead of the snail/cogs, then stop including these in u-s-s.

[Iain Lane (laney)]

Hmm, actually there are a couple of cases here

  - The background chosen by the user from the application is invalid
    + Maybe refuse the selection and keep what we had previously.
    + Or fall back to Unity's default.
  - Externally (via gnome-control-center or gsettings or whatever) an invalid
    URL is set. Could be one of these 'timed' xml files or something else
    altogether.
    + Trust the shell to do the right thing, perhaps? In a GNOME-like
      environment the xml file will be handled correctly and we don't want to
      unilaterally overrule this in u-s-s even if we don't know how to show it.
      But then what do we display? Not sure.

Probably a Q. for design in there.

[Łukasz Zemczak (sil2100)]

This bug actually has a deeper problem related. I guess I will try to workaround it simply for now, but I think that in overall we will need a form-factor independent wallpaper asset for the background and just using the default value of gsettings for fallback. Hard-coding fallback images is generally a bad idea, especially that unity8 also has some values hard-coded, but those are done in per-form-factor fashion - i.e. the geometry is checked, and depending on that a different fallback image is used. I will do the same here, but doing a second batch of hardcoding image names is not a good idea generally.

[PS Jenkins bot (ps-jenkins)]

Fix committed into lp:ubuntu-system-settings at revision 448, scheduled for release in ubuntu-system-settings, milestone Unknown

[Sebastien Bacher (seb128)]

The issue is fixed in saucy with that update https://launchpad.net/ubuntu/+source/ubuntu-system-settings/0.1+13.10.20131011-0ubuntu1