Make `state` a property that automatically calls refresh

[Midnighter]

Example: I have a stack that is in state 'Stopped'. I have a local reference to that stack in the variable stack. I call stack.start(). The state is now indefinitely 'Starting' until I call .refresh(). It's simple to call refresh but it'd be even easier to make state a @property that calls refresh before reporting its (new) value.