Decouple EditorInterface from EditorPlugin

- Simplify some includes in the process.
- Also exposes EditorInterface.movie_maker_enabled as a property.

editor/scene_tree_dock.h

@@ -31,12 +31,13 @@
 #ifndef SCENE_TREE_DOCK_H
 #define SCENE_TREE_DOCK_H
 
-#include "editor/editor_data.h"
 #include "editor/gui/scene_tree_editor.h"
 #include "editor/script_create_dialog.h"
 #include "scene/gui/box_container.h"
 #include "scene/resources/animation.h"
 
+class EditorData;
+class EditorSelection;
 class EditorQuickOpen;
 class MenuButton;
 class ReparentDialog;