Draft: Adding ThOr functor which assigns a random value to the candidate
PURPOSE: Select one random \pi^\pm candidate in the same event as the \pi^0 \to e^+e^-\gamma to be persisted. The Four-vector of the \pi^\pm is needed for the background template.
1^{st} IDEA: Add a Thor functor shuffling the candidates in the weighted relation table and select the candidate, which is situated at the front.
EASIER: ThOr functor assigns a random value between 0 and 1 to each candidate. The candidate with the maximum random value is persisted. The corresponding merge request of the HLT2 and sprucing line additions can be found at Moore!2977 (merged) .