Consider using eslint + prettier

[humphd]

In our Mozilla fork, we're thinking to move to using prettier via eslint to autoformat the code. I'm working with lots of new contributors, and trying to get them to style commits properly is a losing battle. I'm of the mind that doing this with tooling is the better way going forward.

Before we do it, I thought I'd see if you had interest here first; if so, it will make merging easier. Since you've not switched to eslint, this might make sense.

If it doesn't hold interest for you, let me know and we can close this.

[petetnt]

Actually we have already switched to eslint a long while back and I wouldn't have any issues myself to use prettier in combination too. 👍

[humphd]

@dsych is starting this work in mozilla#703. I made a compare branch to show the effect of running grunt eslint using prettier to fix problems. There are some things here that need to be adjusted (e.g., 4-spaces vs. 2, fix javadoc style comment blocks, etc) but everything is configurable. Feel free to chime in with any suggestions on how the configuration should look.

Should I have him move this PR here, or keep it in ours?