Optimise upcomming overview creation

[Raudius]

• Target version: master

Summary

By pre-sorting the cards by due date in the backend we can speed-up the view creation, particularly for instances where many cards have to be loaded.

Checklist

• [ ] Code is properly formatted
• [ ] Sign-off message is added to all commits
• [ ] Tests (unit, integration, api and/or acceptance) are included
• [ ] Documentation (manuals or wiki) has been updated or is not required