Fix broken links in References

[DutchDevOfficial]

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• [d7d9a7] LoRaWAN Backend Interface Specification
• [7c63ac] MXC's Data Economy Whitepaper
• [c63390] MXC SMB Whitepaper
• [b26ba7] Aura
• [7fd55a] NPoS
• [0ec873] Substrate Executing Privileged Functions
• [fa094e] Polkadot Token Economics Payment Details
• [903282] Parity Proof of Authority (PoA) Chains
• [b05a57] Polkadot Token Economics Relay Chain Transaction Fees

Only accessible with permission

• [6fe50e] MXC Roaming Presentation by Aslan on 6th August 2019 including Activation Passive Roaming