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.
Add check for unique shortNames of cuts.

Add check that each cut has an unique shortName, otherwise the
first cut with the corresponding shortName was picked. (issue7)
Add check for axis ranges.

Add check if the lower bound of an axis is above the upper bound
of an axis, because otherwise the axis range is automatically generated
by root.