Core: Allow overriding existing objects in the ConfigServiceLocator.
Corona: Remove response handling from front controller class.

This does not really work as expected when you chain front controller
calls (e.g. when looking for controllers in multiple locations).
Corona: Fix coding style in FrontController class.
Spark: Add base Api class for Facebook.
Spark: Add Facebook Authentication support module.
Spark: Add Facebook User class for shared user handling functionality.