Decouple EditorInterface from EditorPlugin

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

editor/gui/scene_tree_editor.h

@@ -31,10 +31,11 @@
 #ifndef SCENE_TREE_EDITOR_H
 #define SCENE_TREE_EDITOR_H
 
-#include "editor/editor_data.h"
 #include "scene/gui/dialogs.h"
 #include "scene/gui/tree.h"
 
+class EditorSelection;
+
 class SceneTreeEditor : public Control {
 	GDCLASS(SceneTreeEditor, Control);