Remove unused channel

- Be more flexible around device's metadata (match amon schema)
- Don't send through all device when editing, only the edited keys
- Be more careful around posting property_data (don't post it when it's
  not edited)
Merge pull request #528 from MastodonC/feature/null-chan-fix

Remove unused channel
Display uploaded documents
Add migrate job
Fix migrate job and add delete buttons
Better file name display