adding keepStrongVertices option, see ATLHI-483

Fixes ATLHI-483 by adding keepStrongVertices option. Solves issue where decay vertex strongly decaying resonances were not set properly. Keeping these vertices is now the default, but the old behavior can be restored by changing this flag to False in the job options.

Generators/Hijing_i/Hijing_i/Hijing.h

@@ -81,6 +81,7 @@ protected:
   bool m_rand{false};
   bool m_wide{false}; // True allows particles with x,y distributions
   bool m_prand{false}; //BPK mirror event randomly
+  bool m_keepAllDecayVertices{true};
 
   // Limit settings
   double m_partonStoreMinPt{5.0};