Don't allow confusion pairs with the same term and confused term id #2
Description
From quizfreely/api#3:
The API shouldn't allow confusion pairs with the same term and confusedTerm, cause that wouldn't be an incorrect answer.
Quizfreely's IDB API layer also shouldn't allow correct answers as confusion pairs. A pair's term and confused-term shouldn't be allowed to be the same.
(also see quizfreely/quizfreely#57)