Use unity-control-panel when avaliable
indicator-datetime package uses com.canonical.indicator.datetime gsettings namespace, and that namespace is managed by unity-control-panel, not by gnome-control-panel.
Fixes #12087 #13233 #13379
indicator-datetime package uses com.canonical.indicator.datetime gsettings namespace, and that namespace is managed by unity-control-panel, not by gnome-control-panel.
Fixes #12087 #13233 #13379