"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

@@ -184,6 +184,8 @@ int main(int argc, char** argv) {
 
   output.startOfLibrary();
 
+  output.startOfLibrary();
+
   auto const primaryProperties = std::make_tuple(
       beamCode, calculate_kinetic_energy(plab.getNorm(), get_mass(beamCode)),
       plab.normalized(), injectionPos, 0_ns);