Metacity/Mutter stores keybindings as string array to support multiple
bindings per action. Even though multiple bindings are not exposed in
the UI, support keybindings stored as string array by getting/setting
the first element of the array.
https://bugzilla.gnome.org/show_bug.cgi?id=653613
Move most of the horrible GConf monitoring code to a separate
GObject(-ish). While quite ugly, it's not as bad as the code that
used to be there before.
Also fix the setting of KeyEntry->model (or CcKeyboardItem->model now)
to be the correct model (eg. the shortcut model rather than the section
model)