[handler] Add handler registration implementation
[handler] Add handler registration implementation

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