improve the editorial recommendation form

This implements some of the improvements discussed by the Physics College (internal discussion link).

Specifically, here we:

• Make it clear that the authors don't see the remark until after the vote
• Make the remarks for the editorial college required
• Expand the explanations for the editorial college remarks

@jscaux pinging you directly since I'm not sure if you get notifications for this activity.

changed the description

@jscaux do you have any comments on this merge request?

mentioned in commit 6155d4bd

merged