Fix bug re: admin approving a proposal

- Fix bug preventing admins from approving proposals
Add specs for admins proposing, applying for users

- Add specs to test that admins can propose and apply to projects for
  advisors and students after the proposal and submission deadlines have
  passed
Add specs for admins proposing, applying for users
Add admins_acting_for_users specs
Remove duplicated code from some controllers
Add to new interface specs