Extract Constest::unused_problem_codes
Convert 'problem codes exhausted' error from template check to a message
Pass unused problem codes as a simple array
Do not error on duplicate codes while linking problems
Fix problem code validation. Translate error message.
Translate comment. Whitespace fixes.
CATS::Data: Translate comments. Whitespace fixes.
Translate 'problems_link' page
Translate 'answer_box' page