Test binary messages

[kettanaito]

• Add tests for sending/receiving Blob and ArrayBuffer.
• Also, add server-to-client forwarding cancellation tests for Blob and ArrayBuffer. When dealing with binary data, Socket.IO will split a single message event in two: (1) the signaling event (451-[name,placeholder]); (2) the actual binary data. This means the interceptor will also receive two MessageEvent for a single send/emit with binary data.