Theme improve.

* Updated color palette from the Ambiance GTK theme.
* New style for the taskbar with hover highlights.
* Menu icon updated.
* Menu style with hover highlights.
* Calendar widget styled. It must work with any of the two clocks availables.
* Volume popup styled.
* Runner styled.
* New wallpaper, from the Ubuntu Karmic contest, by Kenneth Wimer, released under CreativeCommons license.