Add ESLint, Prettier, auto-changelog

Following our other libraries, we should lint and format this project with ESLint/Prettier.

- Add our ESLint packages as dev dependencies (minus TypeScript and Jest)
- Add ESLint configuration file
- Add Prettier as dev dependencies
- Add Prettier configuration file
- Add `@metamask/auto-changelog` as dev dependency
- Fix any lint violations with changelog (also see https://github.com/MetaMask/eth-token-tracker/issues/51)
- Add `lint` and `lint:*` package scripts

Review the package manifest and the linting and formatting setup used by the repository's other libraries, then compare the changelog with the related eth-token-tracker issue. Add the requested development dependencies, configuration files, and lint-related scripts, and finish when the project passes the new checks without changelog violations.

Written by the indexing model from the issue text.