As a workbench user, I want to be able to improve the collaboration between workbench users. The main goal os this epic is to provide fine-grained control to authoring content and actions.

The first step is to make real use of the contributors tab for spaces and projects. We should support three types of contributors: owner, admin, and contributors (AF-1573).

Each role has some responsibilities on project and space administrations (AF-1639) and also spaces needs to become a real persisted concept, instead of just a logical one. (AF-1572).