Change Backoff Strategy

Backoff Strategy parameters was extracted to config, and default parameters was changed for slowing down reconnection actions and set max available reconnect iterations. Now we can change this parameters by modifying config on instance creation.
Now we have this config structure:

Config{
		BackoffReconnectConfig{
			NumReconnect:    DefaultBackoffNumReconnect,
			Factor:          DefaultBackoffFactor,
			Jitter:          DefaultBackoffJitter,
			MinMilliseconds: DefaultBackoffMinMilliseconds,
			MaxMilliseconds: DefaultBackoffMaxMilliseconds,
		},
		WsConfig{
			PingInterval:         DefaultPingInterval,
			ReadTimeout:          DefaultReadTimeout,
			WriteTimeout:         DefaultWriteTimeout,
			HandshakeTimeout:     DefaultHandshakeTimeout,
			PrivateChannelPrefix: DefaultPrivateChannelPrefix,
			Header:               http.Header{},
		},
}