-Added configuration warning system for nodes

-Added a new "add" and "instance" buttons for scene tree
-Added a vformat() function to ease translation work

scene/3d/spatial_sample_player.cpp

@@ -104,6 +104,7 @@ void SpatialSamplePlayer::set_sample_library(const Ref<SampleLibrary>& p_library
 
 	library=p_library;
 	_change_notify();
+	update_configuration_warning();
 }
 
 Ref<SampleLibrary> SpatialSamplePlayer::get_sample_library() const {
@@ -190,6 +191,16 @@ void SpatialSamplePlayer::stop_all() {
 	}
 }
 
+String SpatialSamplePlayer::get_configuration_warning() const {
+
+	if (library.is_null()) {
+		return TTR("A SampleLibrary resource must be created or set in the 'samples' property in order for SpatialSamplePlayer to play sound.");
+	}
+
+	return String();
+}
+
+
 void SpatialSamplePlayer::_bind_methods() {