Support running the game in Editor via module dll

[gorlak]

• Refactor Input interface to allow the Editor to implement its own input events and deliver them to the game
• Refactor/Integrate GameSystem into Editor (ensure all loaded Assets are released on cleanup)
• Load/Unload the game module into/from the Editor's address space on Project open/close
• Hookup Play/Pause/Stop buttons to GameSystem
• Create World object inside EditorEngine instead of when first SceneDefinition is loaded