Provides numbers that will populate the poverty calculator main chart.
character: Country ISO 3 codes
integer: Reporting year
numeric: Poverty line
logical: If set to TRUE, will interpolate / extrapolate values for missing years
character: Will return aggregated values for predefined sub-groups
character: Welfare type
character: Geographical reporting level
numeric: Units used to express population numbers (default to million)
list: A list of lkup tables
data.table