Add esformatter plugin for automatic formatting

[lshearer]

esformatter—a JavaScript formatting tool with built-in whitespace formatting support that can be pluggable or chained to do about any sort of formatting—supports plugins that enable you to import a shared settings module. An example of this simple type of plugin is https://github.com/bcomnes/esformatter-standard.

By creating an esformatter plugin, we can have automatic in-editor (and command-line) reformatting of code to match the styles enforced by ESLint.

Editor support:

• Atom - pending resolution of Support local versions of esformatter sindresorhus/atom-esformatter#56 so that our custom plugin can be used with the default Atom plugin.
• VSCode - ??
• Sublime - ??