Support group and organization images over remote bucket

[ccancellieri]

Would be nice to have.

From README notes:

2. Currently, only resources are supported. This means that things like group and organization images still use CKAN's local file storage.

Can we discuss how to better implement this? would be nice to have all the assets decentralized

Do you see any other data/asset which should be de-centralized?

[TkTech]

This is in #23 & #25