Allow editors to read reviews and assign and unassign reviewers from the submission summary panel

[NateWr]

Describe the problem you would like to solve
Editors want to be able to read reviews and assign and unassign reviewers without leaving the submissions list, so that they can more quickly manage many submissions.

Describe the solution you'd like
Add buttons to read reviews, assign and unassign reviewers from the reviewers panel in the submission summary panel.

Who is asking for this feature?
This was a recommendation after user tests for #7495.

Additional information
This issue depends on the summary panel (#8883) and showing the review assignments in it (#8891). No mockups are available yet, but the buttons would integrate with the list of review assignments mocked up in #8891.