[Todo] Implement "cool down" timer for heater

[Wh1terat]

The filter needs to be circulating for a short time after disabling the heater in order to cool the heater down. Need to implement some kind of timer to prevent the filter from being disabled too soon.

[Wh1terat]

Kinda implemented - bit of a hack. Still need to find a good way to stop users being able to turn off the filter until the cool down has completed.

    async def async_turn_off(self):
        """Turn heater off and filter 30 secs later."""
        await self.hass.async_add_executor_job(
            self.coordinator.client.set_data,
            self.coordinator.device_id,
            self.info_type[CONF_COMMAND_OFF]
        )
        # Not sure if this is 'naughty' or not
        self.hass.loop.call_later(
            COOLDOWN_TIME,
            self.hass.async_add_executor_job,
            self.coordinator.client.set_data,
            self.coordinator.device_id,
            {MAP_KEYS_INV['filter']: 0}
        )
        await self.coordinator.async_request_refresh()