Kraken websocket support (#264)

* Initial commit. Adds ticker, candle and trade, subscription support

* Adds support for spread and orderbooks

* Adds new currency pair delimiter ("/"), Adds dedicated websocket Connected channel handler, Updates Kraken websocket capability definition, Refines websocket tests to connect and disconnect without freezing, separates WebsocketUnsubscribeEventRequest ChannelID into its own struct WebsocketUnsubscribeByChannelIDEventRequest to prevent bad json WS requests, Adds asset type to orderbook, Kraken WS handles connection better

* Removes duplicate type, reverts config value

* Addresses error returns and changes writeToWebsocket to use byte array. Removes deferred funcs in tests. Increases test listening limit for rare cases

* Fixes verbose log. Rearranges WS Connect async ordering. Fixes DATA RACE. Fixes random okex tests. Ensures Kraken WS tests only connect once

exchanges/okgroup/okgroup_types.go

@@ -1135,12 +1135,12 @@ type GetSwapForceLiquidatedOrdersRequest struct {
 
 // GetSwapForceLiquidatedOrdersResponse response data for GetSwapForceLiquidatedOrders
 type GetSwapForceLiquidatedOrdersResponse struct {
-	Loss         float64 `json:"loss"`
-	Size         int64   `json:"size"`
-	Price        float64 `json:"price"`
+	Loss         float64 `json:"loss,string"`
+	Size         int64   `json:"size,string"`
+	Price        float64 `json:"price,string"`
 	CreatedAt    string  `json:"created_at"`
 	InstrumentID string  `json:"instrument_id"`
-	Type         int64   `json:"type"`
+	Type         int64   `json:"type,string"`
 }
 
 // GetSwapOnHoldAmountForOpenOrdersResponse response data for GetSwapOnHoldAmountForOpenOrders