Create a reference to a GnomePnpIds object to speed up loading
During loading, the singleton GnomePnpIds is created and destroyed 3 times during startup. This means that the pnp.ids is loaded from disk each time and re-parsed. Whilst loading it from disk subsequent times is fast, parsing is not. By keeping a reference at daemon startup ensures it's only loaded and unloaded once per daemon startup-shutdown. This speeds up startup of gnome-settings-daemon by about 400ms.