Use CoreUser schemas instead of CoreUser models in modules

[armanddidierjean]

Subject of the issue

Currently, all modules get CoreUser models from the db, using dependencies like is_user_a_member. These modules don't need to manipulate CoreUser models, as they won't modify them.
Usually, they just use data about the user, like its name.

The model CoreUser contains sensitive information, like the password hash. Some module could accidentally leak them by logging or returning them in the http response.

Proposed solution

Dependencies (like is_user_a_member) could return a CoreUser schema.
If some modules use cruds from cruds_user, we could replace them by utils returning CoreUser schemas.