improve candidate list display
#318 Allow candidates to add links to their profile

The extra fields in the edit_profile form are displayed if the user is a
candidate. When the form is saved, the links are added to the candidate
using the generic foreign key in the Link model.
Move link fields to the end of edit_profile form
Show candidate links in public profile
Fix icon paths and add missing icons

Also use object_links to display them, and move them to be below the
candidate picture and description.