Our ESLint config is out of date with our other repos, and this repo is missing depcheck.

• Copy the versions of our ESLint config packages that the module template is using. If this issue is addressed before Migrate to TypeScript #156 and Migrate from Mocha/Chai to Jest #165, we would want to omit Jest and TypeScript packages.
• Ensure that .eslintrc.js is up to date. If this issue is addressed before Migrate to TypeScript #156 and Migrate from Mocha/Chai to Jest #165, we would want to omit Jest and TypeScript-related config.
• Copy .prettierrc.js from the module template
• Ensure that all lint:* scripts in the module template are reflected in this repo.
• Add depcheck as a development dependency, and copy .depcheckrc.json from the module template.
• Fix lint violations caused by the upgrade. Running yarn lint:fix should automatically fix most of them, but we will need to manually fill in missing JSDocs.