Improve the CLI and add better test coverage.

[philipwalton]

Basically, make it so the CLI can be customized as much as the main browser app.

This should probably happen through the html-inspector-config.js file which should handle any customization as well as calling inspect(). Only call inspect programmatically if there's no custom config file (currently PhantomJS always calls inspect()).

Also make sure to add automated tests (which don't currently exist).