StudentQuiz 4.2.0

• Removed unused migration code affecting the question categories of other existing StudentQuizzes during restore (and thus potential fix for question loss issue)
• Students can now also edit (and not only delete) their comment themselves within the time limit set in the settings (Thank you @lamtranb)
• Fixed various filter options not applying correctly due to past changes
• Fixed tags for questions in a subcategory weren't shown
• Fixed hidden questions are now correctly filtered and so don't have a side effect on the question count and table view anymore
• Removed unused database tables and fields
• Fix missing translation in state change during quiz
• And as always minor fixes and improvements (Thank you @HuongNV13 and @timhunt for your valuable input as always)