js / implement pub/sub in browser

[marcobambini]

@danielebriggi has already implemented the pub/sub in node.js with cf44c29

We also need to implement it with the browser version using websocket (it will talk directly to the gateway and not with the core so that the communication protocol will be much easier than the node.js version).

[jacobprall]

Status? @danielebriggi

[danielebriggi]

@jacobprall , @gionatamettifogo is implementing a scalable version of pubsub using RabbitMQ