Implement routes for /user and improve auth #57

This feature consists of four separate functionalities:

1. Implement routes for user-related functionalities under /user, inluding uploads of profile picture, changing user data like name, surname, and nickname (and ensure it is unique)
2. Allow user to change password viacode sent to an email if account uses basic auth (email, password)
3. Allow user to link social provider as login method if account was created using basic auth (email, password)
4. Improve auth by adding env variable EMAIL_CONFIRMATION that will require user to confirm email by clicking link sent to user's mailbox.