feature: Network layer does not support subscriptions

[AndreiCalazans]

Add custom network layer to support subscriptions.

RelayNetwork: This network layer does not support Subscriptions. To use Subscriptions, provide a custom network layer.
▶ 4 stack frames were collapsed.
./src/subscriptions/NewVoteSubscription.js.__webpack_exports__.a
src/subscriptions/NewVoteSubscription.js:42
  39 |     onError: error => console.log('An error ocurred', error),
  40 |   };
  41 | 
> 42 |   requestSubscription(environment, subscriptionConfig);
  43 | };
  44 | 
  45 | 
View compiled
LinkList.componentDidMount
src/components/LinkList.js:39
  36 | };
  37 | 
  38 | componentDidMount() {
> 39 |   NewVoteSubscription(this.props.environment);
  40 | }
  41 | 
  42 | render() {
View compiled