tor-hsservice: Derive service state from the state of its components.

We need to know the status of each component to be able to report the overall status of the service. Without this change, the service (and its components) have no way of knowing if a given transition is valid: if the state of a component (say, the IPT manager) is Bootstrapping, Recovering or Broken, a transition out of the current state is only valid if it is initiated by the same component that caused the current state (for example, if the publisher sets the state to Recovering, the IPT manager should not be allowed to trigger an overall state transition to Running).

Part of #1083 (closed)