Invitations [PD-496]

One thing I'm not happy with is the process for an invited user if that user tries to create an account for themselves. If they click a link in an invitation, everything works. If they go to secure.my.jobs, for instance, and try to create an account for themselves, the account will already exist and they will have to request a password reset.

Each component was independently reviewed already, but that shouldn't stop the feature from being reviewed as a whole.

All tests pass.