* added unavailability tracker, updated sensor component
* change hass argument position according to position in binary_sensor
* added hass argument to binary_sensor, updated is_on(), it can be UNAVAILABLE now
* updated switch component to support unavailability feature
* updated light component to support unavailability feature
* updated cover component to support unavailability feature
* set _hass property
* added unavailability tracker, updated sensor component
* change hass argument position according to position in binary_sensor
* added hass argument to binary_sensor, updated is_on(), it can be UNAVAILABLE now
* updated switch component to support unavailability feature
* updated light component to support unavailability feature
* updated cover component to support unavailability feature
* set _hass property
* fixed error with wrong arguments number during callback call
* reset unavailability state on new message received from device
* use locks to fix race condition during managing _state property
* overriden state() method for some components to check for STATE_UNAVAILABLE and return it instead e.g. STATE_OFF
* fixed linter
* removed blank line
* use available() method instead of changing _state
* filter motion sensors 'heartbeat', was removed from PyXiaomiGateway
* remove self._hass, use self.hass set by HA on attach
* self.push_data now running in the event loop, use async_schedule_update_ha_state()
* merge fix
* removed accidentally added home-assistant-polymer
* bump PyXiaomiGateway version to 0.8.0
* bump PyXiaomiGateway to 0.8.0
* updated methods names and annotations
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