Issue with study_type = "study", looking for replaced_mode in the df

[iantei]

Encountered an issue with study_type = "study".

The issue is happening because in expand_inferredlabels(labeled_inferred_ct) in scaffolding.py,
we are filtering out with the conditional check as
expanded_labeled_inferred_ct = expanded_labeled_inferred_ct[(expanded_labeled_inferred_ct['mode_confirm'] != 'uncertain') & (expanded_labeled_inferred_ct['purpose_confirm'] != 'uncertain') & (expanded_labeled_inferred_ct['replaced_mode'] != 'uncertain')]

However, the "study" does not have replaced_mode. Resulting in the issue.

Encountered the issue while testing for CO2 emission, this issue has been handled in #152 ea3cd89 by only using mode_confirm as the filter.