renamings in ILifecycle and LifecycleController, etc (see below)

- removed str()
- call operationCompletionCallback when operation is not immediately done
- some docu in ILifecycle
Lifecycle.h broken up -> ILifecycle.h, LifecycleOperation.h
assert that interface and node operations can only be applied to network nodes
link layer: introduced MACBase
MACBase made INotifiable and ILifecycle
link layer: introduce isOperational etc in MACs

also: remove hasSubscribers optimization from PPP, we'll use signals soon anyway