Remove use of jQuery and modernize

[nathansobo]

This is a pretty substantial rework of this package that does the following:

• Convert CoffeeScript to JS
• Use Etch rather than SpacePen for all views.
• Switch tests from legacy built-in infrastructure to Mocha.
• Extract a singleton class and decouple tests from Atom's package management.
• Eliminate Reporter singleton and replace it with an instance variable on the main module.

I did pretty extensive manual testing but it would be great if you could give this a spin @ungb. One known issue is that text editors for the init script, style sheet, config, and snippets aren't opening in the left pane. This is actually an issue in atom/atom and atom/snippets and I plan to fix it there.

[ungb]

@nathansobo Just finished testing various things on the welcome package with your changes. Everything looks good!