Represents average (mean) models.
buildModel() passes on forecasting functions to FcastModel's methods considerBoxCox and considerBootstrap; allows to choose whether forecast intervals should be generated from bootstrapped residuals and whether using Box-Cox transformation and bias-adjustment would result in better overall forecast accuracy; calls a FcastModel's method analyseResiduals which checks whether residuals are not independently distributed and not normally distributed
useModel(fcast_period) calls FcastModel's method executeUseModel to forecast fcast_period-step ahead future; passes on the same fitting and forecasting functions as buildmodel()