exchanges/websocket: Allow configuration of orderbook publish period (#805)

* Allow configuration of orderbook publish period

For some applications that import GCT it's more interesting to be
immediately notified of an exchange orderbook update instead of
only getting notified every 10 seconds. This option allows that
to happen while keeping the previous default.

* exchanges: allow configuration of orderbook update period

exchanges/bithumb/bithumb_wrapper.go

@@ -179,6 +179,7 @@ func (b *Bithumb) Setup(exch *config.ExchangeConfig) error {
 		GenerateSubscriptions:            b.GenerateSubscriptions,
 		Features:                         &b.Features.Supports.WebsocketCapabilities,
 		OrderbookBufferLimit:             exch.OrderbookConfig.WebsocketBufferLimit,
+		OrderbookPublishPeriod:           exch.OrderbookConfig.PublishPeriod,
 		BufferEnabled:                    exch.OrderbookConfig.WebsocketBufferEnabled,
 	})
 	if err != nil {