A slow GitHub no longer holds up Obeya

Obeya keeps an eye on every card whose work went out as a pull request on GitHub, asking GitHub every two minutes and whenever you come back to the page. Those questions used to run one after the other, and the server answered nothing else in the meantime. On a slow network or a busy machine, opening a card, switching canvases or playing a demo video could hang for many seconds. Now the questions run side by side in the background, so Obeya keeps answering at once and still notices what changes on the pull request.