Set a default profile background image
It would be really nice if global admins could set a default image for profile backgrounds, so that if a user hasn't uploaded a custom background image, there's something better than a plain grey box behind their avatar.
We'd use this feature to set a branded graphic as the default background, which would be cohesive with our overall theme & header design.
Please note that we'd want this to have the following restraints:
- Users should still be able to upload their own background, if they choose.
- Existing, user-specific backgrounds should not be replaced with the default
- If we changed the default image, it should update profiles still using the old default, but again leave user-uploaded backgrounds alone.