text: Title: Add a timer and more warnings/protections in imports
  Body: We should have some kind of timer to give users an idea of how long the import process is taking. If it goes beyond some period of time we should notify the user to contact a server administrator to run the import manually or something to that extent. 
  
  Or we should come up with some way to have CTFd pause entirely until the import succeeds, maybe with a special config like `import_in_progress`. 