CLC-2991 Fixed: Expired students should be able to see the MyFinances information

https://jira.media.berkeley.edu/jira/browse/CLC-2991

- Added a new role "ex_student" in the return value for CampusData.get_person_attributes
- Added a "has_financials_tab" attribute to the :student_info hash returned by the UserApi feed
- Added tests to confirm that both active and expired students have their :has_financials_tab returned as true and that non-students get it as false
- Changed view (_navigation.html.erb) to use the has_financials_tab attribute (instead of roles.student) to toggle the "My Finances" tab