Migrate creator from TSLint to ESLint (and prettier)

[AlCalzone]

PR Checklist:

• Provide a meaningful description to this PR or mention which issues this fixes.
• Add tests for your change. This includes negative tests (i.e. inputs that need to fail) as well as baseline tests (i.e. how should the directory structure look like?).
• Run the test suite with npm test
• If there are baseline changes, review them and make a separate commit for them with the comment "accept baselines" if they are desired changes
• Ensure the project builds with npm run build
• If you added a required option, also add it to the template creation (travis/create_templates.ts)
• Add your changes to CHANGELOG.md (referencing this PR or the issue you fixed)

Description:
Since TSLint is going to be deprecated, we switch to ESLint for TypeScript linting. While we're at it, also add support for prettier for automatic formatting.