- use modals
- less proeminent button
- field styling/labels

Fix #923: Use same markdown widget for all content fields (rules, description, reports, notes, etc.)

Discovered when attempting to upload a file with name avatar.JPG

The following error was reported in the logs:
```
File "/app/funkwhale_api/common/serializers.py", line 213, in to_internal_value
     format=PIL.Image.EXTENSION[os.path.splitext(file_obj.name)[-1]],
 KeyError: '.JPG'
```

Reduce size of image by using --no-cache

Fix #348, #474, #557, #740, #928: improved deduplication logic to prevent skipped files during import