Parses 'setting_string' as str formatted in <column>[:<key>]
        and returns str type 'column' and 'key'

def parse_column_key(setting_string):
        """
        Parses 'setting_string' as str formatted in <column>[:<key>]
        and returns str type 'column' and 'key'
        """
        if ':' in setting_string:
            # splits <column>:<key> into <column> and <key>
            column, key = setting_string.split(':', 1)
        else:
            # stores <column> and <value>=None
            column = setting_string
            key = None

        return column, key