The contributors tab for spaces and projects should support three types of contributors: owner, admin and contributor. There must be always only one owner (therefore the owner can't be deleted, only changed), and initially it is the user that created the space or project.

When a project is created, its contributors will be the same as the space it is inside, only difference is that the owner will be changed to the user who created the project.

The roles and permissions of each type will be covered in AF-1639.