Ah.5 - Mini apps native support

Mini apps are small apps that run inside the main app, in the spirit of Telegram or WeChat. This milestone covers the protocol and platform pieces they need: QR codes, push notifications, payment requests, mini apps that interact with each other (one handling Bitcoin Lightning, another handling a purchase), mini app access to native payment methods, warnings about malicious mini apps, and the option to move legally sensitive features out of the core app and into mini apps. The approach could extend to wallets like Trust Wallet or Ledger Live, so that people are attracted to the Nimiq blockchain and not just to one app. The Mini Apps Competition running right now, with $50,000 in prizes, is a first taste of this.