reimplement support for external modules.

[Tim Lunn]

In gnome-3.8 support for external panels has been removed.

I have written a patch to re-implement these, however it has the following limitations.

- modules (i.e. panels with .so files) need to have the desktop file name gnome-'module'-panel.desktop. Although I currently have a fallback in place for 'module'-ccpanel.desktop, since a few extensions seem to use that also.

- launchers (i.e things like language), are loaded from a static list of file names, which is within the patch. I really didn’t want to haul the gmenu code back in. So this seems like a good comprise. A number of tweaks will need to be made to various desktop files however:
   + language-selector: needs an independent desktop file for panel laucher, so we can hide it in Ubuntu GNOME g-c-c, but not apps search
  + ubuntu privacy panel: needs to be set to OnlyShowIn=Unity.
  + ubuntu appearance panel: needs desktop file renamed to suit above format
  + deja-dup and privacy: should be renamed to gnome-*-panel format.
  + there maybe a few others, I havent really done a thorough check here.

- there was a macro, CC_PANEL_REGISTER which is now renamed CC_PANEL_REGISTER_EXTERNAL, I am not sure if any extensions use this, but if they do that will need to be changed.

package with patches is at ppa:darkxst/logind for now

[Jeremy Bícha (jbicha)]

I believe all of this has been done now in Saucy with two exceptions:

1. activity-log-manager will be fixed in the next release (Privacy panel only shows in Unity; standalone version will show everywhere but Unity and will be renamed to something like Privacy Manager to have a different name than GNOME 3.8's new Privacy panel)
2. It looks like the initial indicator-keyboard/ibus work uses GNOME's region panel so we might not need language-selector to be as visible

Feel free to file individual bugs for any new or remaining issues.