Add docstrings to Dao interface and UserDao, add relevant null checks

.gitignore

ImageApplication.iml

src/main/java/NTNU/IDATT1002/App.java

src/main/java/NTNU/IDATT1002/LoggedIn.java

...n/java/NTNU/IDATT1002/controllers/LoggedInController.java

...main/java/NTNU/IDATT1002/controllers/LoginController.java

...ain/java/NTNU/IDATT1002/controllers/SignUpController.java

src/main/java/NTNU/IDATT1002/models/Login.java

src/main/java/NTNU/IDATT1002/models/User.java

src/main/java/NTNU/IDATT1002/repository/Repository.java

src/main/java/NTNU/IDATT1002/repository/UserRepository.java

src/main/resources/NTNU/IDATT1002/logged-in.fxml

src/main/resources/NTNU/IDATT1002/login.fxml

src/main/resources/NTNU/IDATT1002/signup.fxml