Add a built-in implementation of default MC smearing functions

[alekgajos]

The present implementation of MC smearing functions is very generic and allows for smearing with any arbitrary resolution model PDF provided by the user. The cost, however, is that the smearing procedure is computationally expensive as internally the resolution model is constructed anew for every event.

This PR adds the default smearing functions (which so far are the only resolutions models in our use) which can be applied much faster thanks to their Gaussian nature.

Relevant GeantParser parameters:

"GeantParser_UseDefaultZSmearing_bool": true,
"GeantParser_UseDefaultTimeSmearing_bool": true,
"GeantParser_UseDefaultEnergySmearing_bool": true,
"GeantParser_DefaultZSmearingSigma_float" : 3.0,
"GeantParser_DefaultTimeSmearingSigma_float": 80.0,
"GeantParser_DefaultTimeSmearingThresholdEnergy_float": 200.0,
"GeantParser_DefaultTimeSmearingReferenceEnergy_float": 270.0,
"GeantParser_DefaultEnergySmearingFraction_float": 0.044

[wkrzemien]

It looks good to me!