hubers: Add cut on background tracks.

Add cut on background tracks depending on momentum, zfirst and time.
hubers: Add function to get best pi0 candidate.

Add function to get best pi0 candidate. Using a combination of the
highest energetic cluster with all others.
hubers: Add mass parameter for enforceEconservation

Add mass parameter for the enforcing of the energy conservation
with a neutral particle. needed for pi0 analysis. Further cleaning
up of the code.