Binance: Subscribe/unsubscribe response handling (#1444)

* Binance: Fix subscription failures ignored

* Testing: Fix race on shared config singleton

* Config: Privatise Global config var

We should *either* use a private var *or* use an accessor, but it
doesn't make sense to mix paradigms.
Since GetConfig() is well established this instead removes the limited uses of direct public access and adds a Setter

* Zip: Fix test failure on http mocks

internal/testing/exchange/exchange.go

@@ -22,7 +22,7 @@ import (
 
 // TestInstance takes an empty exchange instance and loads config for it from testdata/configtest and connects a NewTestWebsocket
 func TestInstance(e exchange.IBotExchange) error {
-	cfg := config.GetConfig()
+	cfg := &config.Config{}
 	err := cfg.LoadConfig("../../testdata/configtest.json", true)
 	if err != nil {
 		return fmt.Errorf("LoadConfig() error: %w", err)