Replicate "Internal notes" functionality for managing project reviews

[tompollard]

We could consider replicating the "internal notes" functionality that was introduced in #2255 as a simple first step towards implementing peer review functionality.

i.e. We would add a "Reviews" tab to the editorial tools page for Active Projects, like this:

Initially project editors would need to request reviews via email and then post the reviews on behalf of reviewers. We could then work towards more complete peer review functionality by:

1. Allowing PhysioNet users to post reviews to a project upon invitation.
2. Allowing PhysioNet editors to send email invitations to reviewers
3. Introducing an "Awaiting reviews" step to the editorial workflow (between "Awaiting Editor Assignment" and "Awaiting Decision") that would encourage editors to seek external reviewers on all submissions.

@bemoody @lilehman Please let me know your thoughts.

We can implement Step 1 very quickly if you agree this is a good direction.