Port client side code to GDBus

This continues the series of patches for GDBus porting, affecting
all code that accesses remote DBus objects. This includes modemManager,
automount, autorun (for the hotplug sniffer), calendar, network (for
nm-applet only), power, scripting (for perf monitor interface)

https://bugzilla.gnome.org/show_bug.cgi?id=648651