quiz editing: MDL-17454 first attemtp, and MDL-18554

quiz editing: MDL-17454 first attemtp, and MDL-18554

This is a minimal fix for MDL-18554, I have just added a cancel button and made it work.

The more substantial part of this is MDL-17454, trying to make the quiz editing screen behave appropriately when shuffle questions is on. I am sure Olli will have opinions about this and want to change it further. Rought summary:
* When shufflequestions is off, never restrict manual paging, even if questionsperpage is set.
* When shuffle questions is on:
** Always display the quiz with the defined number of questions per page.
** Remove controls to add things except at the end of the quiz.
** Disable most of the order and paging tab, but still allow the question list to be reordered, in case that helps teachers track which questions they have added.
** Still allow questions to be reordered on the edit tab, but when moving the top question on a page up, reorder with the previous question, rather than moving to the previous page.
* Change the status bar, so that the yellow highlight is reserved for alert information. The more informative stuff is now plain, and moved to under the title. To my mind that associates it more closely with the quiz name. Also it moves Total of grades and Maximum grade closer together.
* JavaScript cleaned up. I learn more about YUI every day.
* Some PHP code clean ups that I forgot to commit separately before making substantive changes.