Support repeating meta information columns

Meta information like identifier, contact, property, etc. may occur more than once. When reading from a .1.propcsv.xlsx headers that occur more than once are renamed.

E.g. if there is more than one contact column in the excel file they will be renamed by the conversion to contact, contact.1, contact.2, etc.

A proper solution would be to solve this by using a parameter for pandas. See https://pandas.pydata.org/docs/reference/api/pandas.read_excel.html and search for mangle_dupe_cols. This parameter allowed the cofiguration how to process duplicate columns, however, in the current version it is not implemented.