[API/Pods] Add endpoint to remove an owner from a pod
[PodsController] Add spec for not allowing a non-owner to remove owners from a pod
[PodsController] Mark pod as unclaimed when the last owner removes themself
Fix minor typo.
Merge pull request #114 from CocoaPods/seg-api-remove-owner

[API/Pods] Add endpoint to remove an owner from a pod