Decouple EditorInterface from EditorPlugin

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

editor/plugins/mesh_library_editor_plugin.cpp

@@ -30,6 +30,7 @@
 
 #include "mesh_library_editor_plugin.h"
 
+#include "editor/editor_interface.h"
 #include "editor/editor_node.h"
 #include "editor/editor_settings.h"
 #include "editor/gui/editor_file_dialog.h"