cxx/core/heartbeat: fetch state instead of caching it

Possible workaround for the first issue reported in #125 (closed) - we fetch the state from the FSM every time before sending - this ensures we always get the most up-to-date state. The other direction of communication is however still required since we need to trigger extrasystoles - in the end there is not much win and I'd prefer the old version with the issue identified and fixed...