Config: Refactor version packages (#1887)

* Config: Move config versions to separate pacakges

* Config: Move version tests to blackbox texts

* Config: Protect registerVersion from overflow

* Config: Protect against version already registered

config/versions/v2/v2.go

@@ -0,0 +1,29 @@
+package v2
+
+import (
+	"context"
+
+	"github.com/buger/jsonparser"
+)
+
+// Version is an ExchangeVersion to change the name of GDAX to CoinbasePro
+type Version struct{}
+
+// Exchanges returns just GDAX and CoinbasePro
+func (*Version) Exchanges() []string { return []string{"GDAX", "CoinbasePro"} }
+
+// UpgradeExchange will change the exchange name from GDAX to CoinbasePro
+func (*Version) UpgradeExchange(_ context.Context, e []byte) ([]byte, error) {
+	if n, err := jsonparser.GetString(e, "name"); err == nil && n == "GDAX" {
+		return jsonparser.Set(e, []byte(`"CoinbasePro"`), "name")
+	}
+	return e, nil
+}
+
+// DowngradeExchange will change the exchange name from CoinbasePro to GDAX
+func (*Version) DowngradeExchange(_ context.Context, e []byte) ([]byte, error) {
+	if n, err := jsonparser.GetString(e, "name"); err == nil && n == "CoinbasePro" {
+		return jsonparser.Set(e, []byte(`"GDAX"`), "name")
+	}
+	return e, nil
+}