Editing code comments on a GitHub review comments

[nedtwigg]

• top comment is just "PR Comment"
• lower thing is a "PR Review comment"
• syntax highlighting for "PR review comment" is must-have
• mismatch between Gitcasso's draft model and GitHub's PR Review Draft model is TBD.

• a lot easier if we do these first
  • multi-textarea data model keyed on (url, timestamp) #98
  • modify or replace OverType #99