serialize material identifier

GUI/Model/Sample/ParticleItem.cpp

@@ -41,6 +41,7 @@ ParticleItem::ParticleItem() : ItemWithParticles(abundance_tooltip, position_too
 void ParticleItem::serialize(Serializer& s)
 {
     s.assertVersion(0);
+    s.rw("MaterialIdentifier", m_materialIdentifier);
     s.rw(m_abundance);
     s.rw(m_position);
     s.rw<RotationItemCatalog>(m_rotation);