Emscripten build

[Kukunin]

It'd cool to have emscipten build with instruction.

• separate process of building *.dat file from main compilation
• add authentic UI on HTML
• add progress bar of loading since *.dat is huge
• write instruction

[ataulien]

Instead of putting everything into the dat at compile time, we should use the installer extractor like android uses. Should be pretty simple with emscripten, too.

That way we can offload the huge package from our server and use something like github-pages, which allows only 100mb per site.