Cleanup the design for multi currencies support, use a single nbxplorer instead of two

BTCPayServer/BTCPayNetworkProvider.Bitcoin.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using BTCPayServer.Services.Rates;
+using NBitcoin;
+using NBitpayClient;
+using NBXplorer;
+
+namespace BTCPayServer
+{
+    public partial class BTCPayNetworkProvider
+    {
+        public void InitBitcoin()
+        {
+            var nbxplorerNetwork = NBXplorerNetworkProvider.GetFromCryptoCode("BTC");
+            var coinaverage = new CoinAverageRateProvider("BTC");
+            var bitpay = new BitpayRateProvider(new Bitpay(new Key(), new Uri("https://bitpay.com/")));
+            var btcRate = new FallbackRateProvider(new IRateProvider[] { coinaverage, bitpay });
+            Add(new BTCPayNetwork()
+            {
+                CryptoCode = nbxplorerNetwork.CryptoCode,
+                BlockExplorerLink = "https://testnet.smartbit.com.au/tx/{0}",
+                NBitcoinNetwork = nbxplorerNetwork.NBitcoinNetwork,
+                NBXplorerNetwork = nbxplorerNetwork,
+                UriScheme = "bitcoin",
+                DefaultRateProvider = btcRate,
+                CryptoImagePath = "imlegacy/bitcoin-symbol.svg",
+                DefaultSettings = BTCPayDefaultSettings.GetDefaultSettings(NBXplorerNetworkProvider.ChainType)
+            });
+        }
+    }
+}