More PR improvements #1582

These came up in the Checkout Pull Request PR, but will be addressed separately. Below part of @sguthals's comment:

When we have multiple authors on a commit, this is how the UI looks. What if there are 10 contributors? Also, everything is right aligned, but then at the bottom in the separated section that avatar and text isn't also scooted over. I am OK with this design, but I want to make sure it was deliberate and not coincidental. Maybe more of a question for @simurai

• Done

Do we want reactions to look like this:

I can see how that matches the rest of the aesthetic, but for some reason looks really flat to me? It's also a little strange because I can't click on them, yet they look kind of like buttons? I like the idea of having them, but would it better to wait until we have support for them too?

• Done

Everything here at the top:

Is clickable except for the green open (which makes sense) and the title. The title, for some reason, threw me. I expected to be able to click on it and have it take me to the PR on dotcom. I know that the file path there at the top takes me there, but maybe because I'm used to clicking on titles and I'm used to things in white being links? Similar to how the thing that is a link here is in white and everything else is in grey?

• Done

Should we add a line here between the last PR and more:

Otherwise it looks like the more might be for that single PR?

• Done

Would knowing what branch the PR is targeting be something we want to include here?

• Done