Add Prettier with ESLint integration (#1589)

* Add Prettier, with basic config and ESLint integration

* Apply Prettier to all files using `yarn lint --fix`

* Tell Prettier to ignore an empty text in a test output.

* Run Prettier on JS files not handled by ESLint, and lint them too

.prettierignore

@@ -0,0 +1,5 @@
+examples/build.prod.js
+package.json
+packages/*/dist/
+packages/*/lib/
+tmp/