validate cv results of a scan before db insert and return error to api
[x] model cv res
[x] api rs message
[x] validation -> check exam.total_score with scores of its exercises and respond to api with warning
"Warning: The total score of the exam is unequal to the sum of the scores of the associated exercises"
[x] candidate already exists? -> get candidate due to 1-n relationship during scan save
[x] exam already exists? -> return None aswell and respond to api with error "Exam already exists"
[x] exercise already exists? -> doesnt get that far when exam is already existing, but return None aswell
validate cv results of a scan before db insert and return error to api