Fetch comments on gists, surface in Sublime Text

Need to poll Github Gist API for comments on the Gist they created. This means we need to keep track of when the Sublime Text user creates a Gist and we need to know its ID.

Fetch a Gist's comments and somehow expose them in the editor. Gists don't have line comments, just overall comments, so maybe have an icon somewhere on the editor. Like the orange envelope on Reddit when you have new mail.
