Integrate new topics and grasple exercises in the game

[BorisPST]

** Creating a game **

• Show the available topics by using the newly created system structure of the backend
• Add option to filter topics by study (checkbox, not selected by default)
• Add a search for the topics during selection

** Showing exercises **

• Embed the exercises based on the grasple URL
• Use the new exercise data to set difficulty and number of attempts
• Adjust calculation of remaining attempts (exercise parameters can be refreshed through the grasple embedding but the remaining number of attempts shouldn't change)
• No longer show incorrect modal because we don't have access to the answer directly; instead show a button to go to next question that automatically proceeds after the same time as before

** Game **

• Remove outdated endpoint usage
• At the start of topic send array of mandatory exercises at once, individually answered on frontend and when done proceed with the normal difficulty selection process
• When difficulty is selected, request an exercise from that topic of that difficulty (add new endpoint for this, also needs to keep track of exercises that were already answered)