allow subscription to hotword detection

[flatsiedatsie]

Currently if you want to know if the wake word has been detected, you will need to create a second MQTT client that listen to that event specifically.

It would be great if the wakeword could also be subscribed to somehow via Hermes.

In my case I require this because Snips is unfortunately not able to create audio feedback after hearing the hotword. (The audio settings may not be changed, and pulse audio may not be installed). But Python has no trouble playing a sound. So currently I have created a second MQTT client which plays a sounds through aplay.

It would be great if the extra MQTT client was not required, and all the moments in the dialogue where Snips usually plays a feedback sound could also be taken over through python easily.