[Submissions] Export anonymous collective information about appraisals and assignment offers

This issue regards the creation of (anonynmous) collective information to provide to the authors about the status of their manuscript:

• Appraisals (how many people viewed the paper, votes per category of readiness and qualification)
• Assignment Offers (how many people offered a conditional assignment, of what type, with which attributes...)

This will provide the essential helper methods when generating weekly submission status emails their web UI counterpart.