MDL-11398 - Random questions sometimes ended up with names different from the cateogry they were actually picking from. Also, the same random questoin could be used in more than one quiz, in which case editing that question would change two quizzes unexpectedly. The fix is:
* Don't let the user set the name for random questions.
* Instead force the name to be "Random (catname)" (localised) whever the question is created or saved.
* When a category is renamed, rename all the random questions in it.
* Remove the restriction that Jamie seems to have added in 1.9 that was preventing the category of random questions from being edited.