Move all buttons that generate a reply of some sort (done, ack, reply,
quote) to the comment thread instead of the comment [1].
When there is a draft for a particular comment thread, all reply buttons
are hidden [2]. For example, if you click reply, you cannot click done
on the same thread, unless you remove the draft.
Each thread can have up to 1 draft. It's also worth noting that if a
thread has a draft, and the user clicks on the line or 'c' at the same
range, the existing draft will switch to 'editing' form.
[1] With the exception of "please fix" for robot comments.
[2] In this case, The please fix button will be disabled when other
reply buttons are hidden.
Feature: Issue 5410
Change-Id: Id847ee0cba0d0ce4e5b6476f58141866d41ffdad
2c602323e1