Add categories for gender

[CarolinOdebrecht]

The skript checking for metadata of the already included texts check for female and male category. We might also have cases where we have undefined or mixed categories, cf. ODD:

                            <valItem ident="M">
                                    <desc>male author</desc>
                                </valItem>
                                <valItem ident="F">
                                    <desc>female author</desc>
                                </valItem>
                                <valItem ident="U">
                                    <desc>author sex unknown</desc>
                                </valItem>
                                <valItem ident="X">
                                    <desc>author sex mixed</desc>
                                </valItem>