Write indicator list sheet

Usage

write_indicator_list_sheet(wb, sheet_name, billion, start_row, start_col)

wb: a openxlsx workbook to be edited.
sheet_name: character name of the sheet to update
billion: Billion indicator names to return, either "hep", "hpop", "uhc" , or "all".
start_row: integer start row of styling. Passed to openxlsx::addStyle()
start_col: integer start col of styling. Passed to openxlsx::addStyle()