Modify stylesheet system to allow 1 manager per view controller.

The style manager associated to this view controller.
 If we find a style file named TheControllerClass.style, we'll create a stylemanager that will load this file
 as the root style file for this controller. This means if you have dependencies on other .style file,
 you'll have to import them in your TheControllerClass.style file to get the inheritance to work properly.
 If we do not find TheControllerClass.style, and your controller is in a container or spitter, it'll use it's containers style manager.
 else we'll get the defaultManager

To ensure backward compatibility, we first check if this controller has a style defined in the default manager. if so, we use this default manager.