Modifying QuestionnaireAdminService and QuestionnaireResponse

[alessandriniluca]

This issue is a reminder for @mattia1p: I am modifying the two classes: Changes in the entity:

• I made the query parametric, in order to reuse it in both ProductUserService and QuestionnaireAdminService, please when merging accept my changes;

Changes in the service:

• I propose to change a little bit the method already implemented by @sam98uele: I can return the list of names of the people who submitted the questionnaire, in order to do not have to detach elements and setting password to null, and in order to avoid throwing exception NoUserException when no user compiled the questionnaire: you will just get an empty list, and you will just need to perform a check in the frontend, without raising exceptions; ( if you agree, I think that in this way the code will be more readable when explaining the project during the exam)

[sam98uele]

I propose to change a little bit the method already implemented by @sam98uele:

@alessandriniluca Which method are you referring to?

[alessandriniluca]

"getUsersSubmittedQuestionnaires" in "QuestionnaireAdminService"