In https://github.com/babel/babel/issues/9511 (and #9495 is another symptom), @PavelKastornyy reported a node crash becaue the JavaScript heap run out of memory. The problem was that their code was adding enumerable properties to `Object.prototype`: it is something that shouldn't be done, but Babel shouldn't make node crash if someone adds them.
I reduced down the problem to `for...in` loops in `@babel/traverse` that grew the memory consumption exponentially because of that unexpected properties.
* .prettierrc: full configuration for Prettier
This way, contributors using different-from-default settings will still
use the correct prettier settings
* Makefile: also lint .babelrc.js
* Makefile: also prettify .json files
* Exclude package.json files and correct build dir
* Add more default options to prettierrc and load it in cli
This avoids prettier looking up the config for each file
* Format json
* Update prettier and eslint and reformat codebase
* Remove obsolete file
* Add comment
