Handle anonymous submissions with users that created accounts (or have partial applications) better

[evan10s]

These are often people who started an application but didn't finish and then end up doing walk-up registration at the event. Perhaps the partial application should be discarded / marked null and the new application accepted.

[petschekr]

Also applies to people (especially team members) who have created an account on registration and then must use a different email for walk-up registration