Function `import_station_list_from_csv_file()` needs to check if all necessary columns are present

Currently, the function import_station_list_from_csv_file() assumes that all necessary data columns are present in the CSV file. This can cause errors if one column name is wrongly spelled or missing. The function should therefore check for the existence of the all columns: network-code, station-code, location-code, longitude, latitude, elevation, start-time, and end-time.