Uses `lookup_table` data to add in questions within a section that were unanswered (and therefore missing from the original JSON data).
add_section_variables(data, lookup_table)Dataframe with columns "section", "variable", and "exp_num".
Dataframe with columns "section", "step", "variable" , and "label" used for user-friendly section and variable display. "step" maps desired "section" names. "label" maps desired "variable" names.