This function creates the object that is returned from impute(). Essentially it is a glorified wrapper around list() ensuring that the required elements have been set and that the class is added as expected.
imputations: A list of imputations_list's as created by imputation_df()
data: A longdata object as created by longDataConstructor()
method: A method object as created by method_condmean(), method_bayes() or method_approxbayes()
references: A named vector. Identifies the references to be used when generating the imputed values. Should be of the form c("Group" = "Reference", "Group" = "Reference").