Add a DecFile of Lb2pKKK,PHSP,Charmless,Cocktailed

This DecFile contains decay \Lambda_b^0\rightarrow pK^-K^+K^- via three different processes of fraction 1:1:1:

1.\Lambda_b^0\rightarrow (\Lambda(1520)\rightarrow pK^-)(\phi\rightarrow K^+K^-), PHSP

2.\Lambda_b^0\rightarrow pK^-(\phi\rightarrow K^+K^-),PHSP

3.\Lambda_b^0\rightarrow pK^-K^+K^-,PHSP

Already tested locally.