[router] Add license and rewrite signatures in Core.go
[router] Add license and rewrite signatures in Core.go

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