Move group and owner setting to management panel

[etj]

At the moment the group and owner setting are editable in the metadata page.
Such info are used to assign privileges on the resource, and are not only descriptive.

We should leave the metadata page only to edit informative elements, while privileges should be edited in a different place, using different access grants and different API wrt to the metadata.

This issue also addresses the frontend

Backend:

• remove owner and group from the metadata editor
• make sure API exists for updating group and owner

Frontend:

• make owner and group editable in the management panel, according to specific privileges.