Created the class BaseEngine and FlashEngine.
It's now possible to override the implementation of the Engine singleton object.
Remove the stage code from the FlashMainWindow (it's now in the FlashEngine class).
All the "friend class Engine" declaration have been switched to "friend class BaseEngine"
Added the implementation override mechanism to PlatformFlagger.h
Added the new files to the Flash makefile.
Prevent the FlashHelper.h from being include on the wrong platform in EntityFactory.