Flashcard activity functionality

1) If "require all cards are known" is checked, then students will never get a completion state. This is true if student is doing free play or Laitner. I have had a student reporting that even when they moved all cards to the easy set and looked at all cards in free play, that the flashcard activity still reports 1 card remaining and will not give them completion credit.

2) Changes to the completion settings are somewhat ignored when "Require viewing all cards" is checked. Specifically, the number below the checkmark indicating the number of cards to be known cannot be set to anything but 999. If it is set to anything else and saved, then the next time the settings are edited, the number returns to 999. This means that partial viewing cannot be used for completion.

3) Lastly, with every other plugin, changes to completion rules contain a warning that doing so will affect those who have already completed it. In other words, there is an unlock completion button. The flashcard activity has no completion button.