Change _convert_custom_fields_to_struct function...
Change _convert_custom_fields_to_struct function...

that is called for each row of the uploaded file into _create_field_map method of _Importer object, called only once per import.

While in the area move a couple of other functions only called from _Importer to being methods on _Importer.

dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq