Update EndVertex Definition for MCParticle

Adds PairProduction and Annihilation as cases for EndVertex and prefers these and decay vertex types over hadronic interaction.

Was presented here

Resolves #188 (closed)

Event/MCEvent/include/Event/MCParticle.h

@@ -165,6 +165,8 @@ namespace LHCb {
     /// Retrieve (const)  Vector of pointers to decay vertices
     const SmartRefVector<LHCb::MCVertex>& endVertices() const;
 
+    const MCVertex* goodEndVertex() const;
+
     /// Update  Vector of pointers to decay vertices
     MCParticle& setEndVertices( SmartRefVector<LHCb::MCVertex> value );