"Need for writing first interaction information"

Solves #639 (closed)

Writes out the

• pdg ID
• position
• momentum vector
• time
• dX

examples/cascade_examples/em_shower.cpp

@@ -181,6 +181,8 @@ int main(int argc, char** argv) {
   auto sequence = make_sequence(emCascade, emContinuous, longprof, observationLevel, cut);
   // define air shower object, run simulation
   TrackingType tracking;
+  
+  output.startOfLibrary();
 
   output.startOfLibrary();