[in memory storage] Implement better broker in-memory storage
[in memory storage] Implement better broker in-memory storage

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