Add a city field to User model

[weihanwang]

1. add city : string | null field to the User model
2. add an input box on /profile page to update city they live in. label text should be "居住的**城市或者国家+城市”
3. add another input box to update wexin
4. another to update sex. give only two options 男 and 女

Note that the /profile page was developed very long time ago and may need some code refactoring before adding new functions. For example, it should be updated to use EditableWithIconOrLink for text fields. The PR that refactors existing code should be separate form the PR that adds new logic.