R1:26dd2a0eef13

Allow ApplicationTransaction comments to be edited and deleted

Summary:
Allows you to edit or delete comments in appplications which support ApplicationTransactions.

UI/UX stuff:

- The dialogs are rough but I want to do a dialog design pass more generally, @chad has some mocks.
- When you add new mentions via edit, they don't currently count as mentions. I'm not sure what I want to do about this.
- When you edit or delete a comment, we do not publish any notifications about it. I think this is…