Change "gender" to "sex"

A valid notion from FB discussions:
“Could you change 'gender' to 'sex'? If you want to make it about
'gender identity' you need to say woman/man instead of female/male
(female is the biological sex, woman is the gender), and then you need
to include trans woman/man, or just leave a field for 'other'. I
recommend using 'sex' instead. Also pls 'female' first, that's
courtesy. And please an 'other' field for politics.“

https://www.facebook.com/groups/hitchgathering/permalink/981437525203147
/?comment_id=981723948507838&offset=0&total_comments=5

Will remain as ‘gender’ at the DB, but it shouldn’t be too confusing,
it’s just label in one place at profile editing page. ;-)