Adds an existing Camera into the Camera Manager.
The Camera should either be a
Phaser.Cameras.Scene2D.Camera instance, or a class that extends from it.
The Camera will have its
roundPixels property set to whatever
CameraManager.roundPixels is. You can change
it after addition if required.
The Camera will be assigned an ID, which is used for Game Object exclusion and then added to the manager. As long as it doesn't already exist in the manager it will be added then returned.
If this method returns
null then the Camera already exists in this Camera Manager.
The Camera to be added to the Camera Manager.
Set this Camera as being the 'main' camera. This just makes the property
The Camera that was added to the Camera Manager, or
null if it couldn't be added.