Add emscripten support

[bugra9]

Related issue: https://github.com/CartoDB/mobile-sdk/issues/510

• Install Emscripten (3.1.17)
• Change src/embind/embind.js with https://github.com/bugra9/emscripten/blob/embind-overloading-support/src/embind/embind.js
• Build mobile swig https://github.com/bugra9/mobile-swig/tree/emscripten-support
• cd scripts
• python swigpp-emscripten.py
• python build-emscripten.py
• cd ..
• ./scripts/emscripten-dev/server/server-localhost
• Visit http://localhost:8000 with your browser

[bugra9]

@mtehver, I implemented your suggestions and updated the demo site. Additionally, the listeners now work.