Transfer ownership end point
Transfer ownership end point

closes #3426
- added transfer ownership endpoint
- added owner to roles.permissible
- manually removed owner from roles.browse
- removed hard coded author role
- fixed tests that were passing due to hard coded author role
- added testUtils.setup(‚roles‘)

JohnONolan/Ghost-Admin,acburdine/Ghost-Admin,dbalders/Ghost-Admin,kevinansfield/Ghost-Admin,kevinansfield/Ghost-Admin,airycanon/Ghost-Admin,dbalders/Ghost-Admin,TryGhost/Ghost-Admin,airycanon/Ghost-Admin,JohnONolan/Ghost-Admin,acburdine/Ghost-Admin,TryGhost/Ghost-Admin