Manage default user profile fields on the same way that is possible for custom profile fields, e.g. hide, show, make them mandatory etc.
Improvements should include:
- each of the functionality that is possible for custom user profile fields
- rename the fields (change label of the field)
- change order of the fields (move up and down)
- make a field mandatory
- show/hide field
- display on signup page
- should be unique etc.