Backend: blacklist blockstream electrum servers

Blockstream electrum servers doesn't support sending
verbose transactions, we use this functionality
for getting confirmations of a transaction, this
causes geewallet to crash.

Blockstream/electrs#36

src/GWallet.Backend/Server.fs

@@ -172,6 +172,7 @@ module ServerRegistry =
             // as these servers can only serve very limited set of queries (e.g. only balance?) their stats are skewed and
             // they create exception when being queried for advanced ones (e.g. latest block)
                 server.ServerInfo.NetworkPath.Contains "blockscout" ||
+                server.ServerInfo.NetworkPath.Contains "blockstream" ||
 
             // there was a mistake when adding this server to geewallet's JSON: it was added in the ETC currency instead of ETH
                 (currency = Currency.ETC && server.ServerInfo.NetworkPath.Contains "ethrpc.mewapi.io")