Add now plugin that show the current team

[nicobarray]

Hi everyone :)

First of all, a quick screenshot:

the now logo with the current username on its right

Rational

Because I always switch between at least 2 now teams, I want to know which team I use right now (too many time I deployed my projects on the wrong now team 😅 )

This PR contains just that: a now plugin that shows the current team used (or the now user if none is activated).

Some informations:

• I first wanted to execa the now cli to get the up to date account informations, yet I could not made it work (maybe an issue with the code running in the render thread ? I'm not versed in electron subtleties, maybe it was a simple error that could be fixes)
• Then I decided to check the now cli code to see if I could fetch the current user informations, and it was possible through /www/user and /teams routes on the now endpoint used by the official cli.
• The now plugin fetches each minute those endpoint to deduce the current user and renders it next to zeit logo ▲

I think it is straightforward enough, yet feel free to discuss/ask me anything about the implementation, I'll be happy to update/explain anything.

Thanks for your time.