Fix editor always redrawing

-Only update rendering settings when project settings change
-Fixes the update spinner (and editor rendering) updating all the time.
-Added a "project_settings_changed" signal to EditorNode and EditorPlugin

editor/project_settings_editor.cpp

@@ -55,6 +55,7 @@ void ProjectSettingsEditor::popup_project_settings() {
 }
 
 void ProjectSettingsEditor::queue_save() {
+	EditorNode::get_singleton()->notify_settings_changed();
 	timer->start();
 }