Have you tried:
cd ~/catkin_ws/
rm -rf build devel
catkin_make
source devel/setup.bash
Also, look for and remove any compiled python files (.pyc) files in your src folder, as indicated by @duckfrost.
Update:
I have just noticed that your package folder is named action_quiz, but in some part of your code you are referring to actions_quiz. This is probably why you cannot import; you need to correct this, ensuring the package is named as specified in the quiz instructions.
I suggest you create another package named actions_quiz, copy in your code and files from the other package, do the necessary modifications, remove the other package and compile again. PS: never copy CMakeLists.txt and package.xml to avoid errors.