fix SCREEN_WAKEUP behavior

[dtreskunov]

There were two issues.

First: in my case, the SCREEN_WAKEUP socket notification was being sent from node_helper.js of another module. The browser code in MMM-PIR-Sensor.js would receive this notification and relay it using the sendNotification function. However, the handler on the server-side in node_helper.js would not see it since it is only responding to notifications sent via sendSocketNotification.

Second: after the screen was woken up, it would never go back to sleep unless the PIR sensor reported some movement followed by no movement.