feat(cli): Add support for Prettier

[daffl]

This pull request adds support for Prettier in a generated application and for the generator to write files in your current Prettier configuration.

To change the Prettier configuration like use of semicolons, trailing commas, line width etc., update the .prettierrc, then run npm run prettier to format all existing files. Subsequent feathers generate commands will write files with the current settings.

Related to #2679