Fix stub for Blob in engine

[docEdub]

Overview

The Blob function is currently stubbed in Babylon.js nativeEngine.ts.

Implement the Blob function so its behavior matches current browser implementations.

Notes

This task was originally captured in issue #62.

[bghgary]

Try to remove the stub and see if everything still works.

[CedricGuillemet]

Try to remove the stub and see if everything still works.

It doesn't:

Running Light Projection Texture
Exception thrown at 0x00007FFFF19B567C in Playground.exe: Microsoft C++ exception: Js::JavascriptException at memory location 0x000000062603B680.
ReferenceError: 'Blob' is not defined