'System status (:py:class:`SystemStatus`).
The status has a ``state`` property with one of the following values:
* ``UNINIT``: Uninitialized system, state is unknown.
* ``BOOT``: System is booting up.
* ``CALIBRATING``: System is calibrating and not flight-ready.
* ``STANDBY``: System is grounded and on standby. It can be launched any time.
* ``ACTIVE``: System is active and might be already airborne. Motors are engaged.
* ``CRITICAL``: System is in a non-normal flight mode. It can however still navigate.
* ``EMERGENCY``: System is in a non-normal flight mode. It lost control over parts
or over the whole airframe. It is in mayday and going down.
* ``POWEROFF``: System just initialized its power-down sequence, will shut down now.'

@property
def system_status(self):

    return {0: SystemStatus('UNINIT'), 1: SystemStatus('BOOT'), 2: SystemStatus('CALIBRATING'), 3: SystemStatus('STANDBY'), 4: SystemStatus('ACTIVE'), 5: SystemStatus('CRITICAL'), 6: SystemStatus('EMERGENCY'), 7: SystemStatus('POWEROFF')}.get(self._system_status, None)
