clean up devices upon migration

[zven]

Description

Upon migrating to the new OSEM version we should clean up all those old devices! It comes down to the question: How do we handle stale accounts and devices?

Use cases

• Users without boxes are not migrated.
• Devices that don't have any measurements are archived upon migration.
• Archived devices are not shown anymore by default.
• Devices without users: Mark as orphaned. Why? -> There might be devices that are part of old campaigns that are still contributing measurements but are not actively managed anymore. In order to not break those, we mark them as orphaned.

Implementation ideas (optional)

• introduce archived state
• introduce orphaned state: Let's do this by simply assigning the email address orphaned@opensensemap.org

Additional information (optional)