Merge pull request #16 from efernandesng/master

Use MetaBackground to manage background image or colors.
wm/plugin: Workaround gnome-control-center hackery

When gnome-control-center sets a colour for a background, it puts the
setting into wallpaper mode, using a noise pixmap. The desired behaviour
is obviously to show a colour, but this is GNOME specific behaviour.

When we detect this behaviour, we simply workaround it, display the colour,
and do not display the noise pixmap. We *may* support the noise pixmap
and colour combination in the future.
wm/plugin: Gracefully handle .xml slideshow failure

We now just fallback to a randomly coloured wallpaper if we're unable
to deal with the wallpaper (i.e. an XML file)
Incorporate gvc into tree

We'll need to use gvc to provide a sound applet, as it is pretty much
the de facto within GNOME.