Provides several methods to normalize quantitative data from
a MSnSet object.
They are organized in four main families : Strong Rescaling,
Median Centering, Mean Centering, Mean CenteringScaling.
For the first family, two sub-categories are available : the sum by columns
and the quantiles method.
For the three other families, two categories are available :
"Overall" which means that the value for each protein
(ie line in the expression data tab) is computed over all the samples ;
"within conditions" which means that the value for each protein
(ie line in the exprs() data tab) is computed condition
by condition.