show currently open drafts in the GitCasso popup

[nedtwigg]

• clicking the GitCasso popup should display a list of all comment drafts in currently open tabs
• clicking a comment draft should bring that tab into focus
• there should be a checkbox that says [ ] click here to save comment revision and submission history
  • clicking that checkbox brings you to save revision and submission history of comments #26

[nedtwigg]

the remaining TODO items have been broken out into their own items