poloniex: websocket update (#659)

* poloniex: websocket update with debug output and currency tracking system

* linter: fix issues

* nits: Addr

* poloniex: govet fix

* nits: addr

* Bittrex: Fix fee test

exchanges/account/account_types.go

@@ -47,3 +47,12 @@ type Balance struct {
 	TotalValue   float64
 	Hold         float64
 }
+
+// Change defines incoming balance change on currency holdings
+type Change struct {
+	Exchange string
+	Currency currency.Code
+	Asset    asset.Item
+	Amount   float64
+	Account  string
+}