enable stricter eslint rules

[rhelmer]

I'm not sure what the gold standard is nowadays, but we should ratchet it up a bit, like always requiring braces around if/then/else statements and other potential safety issues.

I'm less concerned about style in general but it'd be nice to pick something comprehensive instead of a ruleset we need to maintain, since it's not very productive to argue about style nits in reviews :)

[jonathanmayer]

https://github.com/dustinspecker/awesome-eslint

🤷‍♂️

[hamilton]

I personally would opt for the Airbnb rules which I've used in the past. Many sensible defaults, and we can turn off the ones that are not joyful for us.

[jonathanmayer]

Fine by me.