Add sex

Summary:
We will need it for intl.

I've put it to User instead of UserProfile to be easier accessible.

Test Plan:
Apply SQL patch.
Change sex to Male.
Change sex to Unknown.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Maniphest Tasks: T1139

Differential Revision: https://secure.phabricator.com/D2287