MDL-45336 qtypes: use existing strings from core or own plugin
MDL-45336 questionbank: use core strings instead of quiz

AMOS BEGIN
 CPY [categories,mod_quiz],[categories,question]
 CPY [category,mod_quiz],[category,question]
 CPY [export,mod_quiz],[export,question]
 CPY [import,mod_quiz],[import,question]
 CPY [unusedcategorydeleted,mod_quiz],[unusedcategorydeleted,question]
AMOS END