lifecycle: Added status submodules to nodes and interfaces.
lifecycle: Separated carrier state and requested interface state.

Added hasCarrier, setCarrier, isBroughtUp and isUp functions.
lifecycle: Added handling node and interface status to ethernet MACs.
lifecycle: Added handling node and interface status to PPP.
lifecycle: cosmetics.
lifecycle: removed status from StandardHost, NodeBase provides it.
lifecycle: Extended example with shutdown/startup of client and router.