Compact Discussions #2143

Problem

Right now on GitHub there is tons of visual noise around even a single inline comment on a diff:

<img width="1018" alt="Screen Shot 2019-06-09 at 12 20 55 PM" src="https://user-images.githubusercontent.com/952783/59163146-be6a6900-8ab1-11e9-8ff4-b982f0d06490.png">

Proposed Changes

Like why do we need double borders:

<img width="1006" alt="Screen Shot 2019-06-09 at 12 21 12 PM" src="https://user-images.githubusercontent.com/952783/59163157-eb1e8080-8ab1-11e9-8779-95b886265696.png">

Why does "Resolve Conversation" need its own line:

<img width="1003" alt="Screen Shot 2019-06-09 at 12 21 37 PM" src="https://user-images.githubusercontent.com/952783/59163162-025d6e00-8ab2-11e9-96ea-a20f09ebea00.png">

If there's only a single comment, why even have the reply line? Just turn it into a button (reactions are already there...):

<img width="1005" alt="Screen Shot 2019-06-09 at 12 22 55 PM" src="https://user-images.githubusercontent.com/952783/59163176-1c974c00-8ab2-11e9-97f3-497f0cf2c59c.png">

Resolve Conversations could also be a button or it could get the dropdown treatment:

<img width="1006" alt="Screen Shot 2019-06-09 at 12 23 53 PM" src="https://user-images.githubusercontent.com/952783/59163187-5d8f6080-8ab2-11e9-99f3-61ccedc1175a.png">

This change would take the above comment from taking up 240px of vertical space to 120px.

On a pull request with 40 comments, this makes a huge difference.