Exo.Spine.Controller: Fixed a ref bug with addChild and added a mechanism for setting the nodeId
Exo.Spine.Controller: Added childById and descendantById functions
Exo.Spine.Controller: Added null & undefined checks/exceptions to addChild
Exo.Spine.Controller: Added a new boolean option 'childrenCanActivate'
Exo.Spine.Controller: Fixed a bug in descendantById and added a function to set the nodeId
Spec: Added a bunch of new specs to Exo.Spine.Controller