general: use reactive design patterns, with RxJS or highland.js

[jbilcke]

This could be used for a lot of things in ATGC, like communication between the server and the client, or communication and wait/synchronization between modules

(eg. to solve the problem of the egg and the chicken, as we have now with atgc-core-player and atgc-bunde-*modules)

highland.js feels a bit like lazy.js / lo-dash / async: it has a simple API, less verbose than Rx, so it is quick to grasp and quite intuitive to use

However RxJS feels more complete, like a standard library (eg. lot of time-related sync features). It covers a variety of use-cases that could help for our game-related issues