New selection -> Split command

src/libslic3r/Model.hpp

@@ -94,6 +94,8 @@ public:
     void delete_volume(size_t idx);
     void clear_volumes();
 
+    bool is_multiparts() const { return volumes.size() > 1; }
+
     ModelInstance* add_instance();
     ModelInstance* add_instance(const ModelInstance &instance);
     ModelInstance* add_instance(const Vec3d &offset, const Vec3d &scaling_factor, const Vec3d &rotation);