[feature/manager] Implements HandlerManager (ListDevices still missing)
[feature/manager] Implements HandlerManager (ListDevices still missing)

jvanmalder/ttn,TheThingsNetwork/ttn,mgranberry/ttn,TheThingsNetwork/ttn,mgranberry/ttn,jvanmalder/ttn,jvanmalder/ttn,TheThingsNetwork/ttn,mgranberry/ttn,LoRaWanSoFa/ttn,LoRaWanSoFa/ttn