breaking: Ability to pass multiple MC files per channel and const correctness

[KSkwarczynski]

Pull request description

Now code instead of
mtuplefile: "numu_x_numu"
expects
mtuplefile: ["numu_x_numu"]

This allows to pass multiple files per channels, which is getting increasingly needed by DUNE, but I imagine HK will benefit as well.

Need to merge: mach3-software/MaCh3Tutorial#236 first

Changes or fixes

• Now getters correctly follow const correctness
• Removed get Xvar/Yvar name now we should use GetKinVarName
• Target and Mode are not longer part of EventInfo, now they can be acessed via ReturnKinemPar
• Move some public function to private/protected
• Removed sanitise input from ProduceToys

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