Implement customizable gender list in organization

[jsangmeister]

organization.update allows to update the list of allowed genders: https://github.com/OpenSlides/OpenSlides/wiki/organization.update. This should be implemented in the organization settings view so the allowed genders can also be updated in the client. Since it is a list of strings, a nice UI solution has to be found to display this.

[emanuelschuetze]

closed - reason see #3101