Show error screen if WebSocket fail to connect on initial load

[richardfxr]

The canvas is rendered even when a WebSocket connection cannot be established with the Centrifugo server. An error screen should be shown instead as the application is not functional without this connection.

[richardfxr]

Both the Centrifuge WebSocket connection and subscription must successfully connect before the canvas can render. If either of the connections fails, the error screen is displayed. If the connection is re-established, the canvas will render as usual.